PART II Agricultural science (SOIL SCIENCE)

PART II

SOIL SCIENCE

2: THE SOIL SCIENCE

2.1 Introduction to soil science

2.1.1 Introduction

2.1.2 Soil formation

2.1.3 Weathering

2.2 Soil and its components

2.2.1 Introduction

2.2.2 Physical properties and its constituent

2.2.3 Soil moisture contents

2.2.4 Soil H₂0 classification

2.3 Soil chemistry

2.3.1 Introduction to soil chemistry

2.3.2 Soil calculations

2.3.3 Soil reaction

2.3.4 Soil PH

2.4 Fertilizer and Manure

2.4.1 Organic manure

2.4.2 Inorganic fertilizer

2.4.3 Fertilizer calculation

2.4.4 Fertilizer application

2.5 Water supply, Irrigation and Drainage

2.5.1 Introduction

2.5.2 Water supply

2.5.3 Irrigation

2.5.4 Drainage

SOIL SCIENCE

PART II: SOIL SCIENCE

This is the branch of Agriculture which deals with properties of soil and material constituent to it in order plant to grow.

SOIL SCIENCE

2:1 INTRODUCTION TO SOIL SCIENCE

2:1:1 The soil

The soil is the thinner upper layer of the earth’s crust. It’s the weathered part of the earth’s crust in which plants and animals live.

The soil consist of many things that is particles, plants remains, minerals that all lead growth of plants. Peoples who grow crops pastures, vegetables and flowers who is famers ,market gardeners or home gardeners ,they know what is the importance of types of the soil on how can lead their success .some soil are deep other are hard and others are sandy this is because of the types of soil.so by thus means soil is determined by its type or we can say its properties.

Importance of soil to the growth of plants

Ø Its supplies the plants with water

Ø Its hold the plants in position

Ø Its supplies the plant with minerals so that food can be made

The bellow section show how soil look like as you dig small portion of land reach some different in horizons of the soil

The figure above show that generalized vertical section of the land, that way observed when a deep hole is dig in soil constituent at an area. This show how soil is look like and on how soil is much necessary for plant growth

The above figure explain about soil profile

Let as introduce the concept of soil profile

The soil profile :these is the arrangement of soil according to layers

The above fig show soil profile and it’s layers, so let us discuss a little beat about soil profile

The layers of soil profile

A-horizon: it contain humus (remains of plants and animal) it’s part contain nutrition in the soil

B-horizon: it contain fine particle, small particles of soil, and alleviation take place in this layer

Alleviation : this is the accumulation of minerals in the soil ,the main minerals in this layer is Iron , zinc, magnesium, silicon and aluminum .B-horizon consist of B1,B2,B3

C-horizon: This layer consist of large particles of the soil that also weathering take place so there small particle also

D-horizon (Bedrock): this is the hard rocks that is the source of large particle in horizon C under the action of force and causes of weathering

The soil: in explanation it may be very deep profile consist of many thing but simply is just the upper layer of crust that help growth of plants

2.1.2 SOIL FORMATION

Introduction: the large particle formed from parent rocks as well as small particles generated

that large one.

NB: Water present in soil leaves from rainfall and underground water reserves while air

originates from atmosphere.

Organic water and living organism are one present in soil as it constituent.

Ø All this are constituents that form soil but organic matter or minerals generate from parent rock by weathering process.

Qn: so, what is soil formation?

SOIL FORMATION: Is the genesis or evolution at the soil from the parent materials or Bed rock. It takes place continuously.

Ø It takes place through weathering process. Example chemistry, physical and biological process, chemical process are hydrolysis, hydration, acidification, oxidation –reduction reactions, dissolution, expansion and construction.

Ø All this process form small units which combines with organic matter, living organism, water and air to form soil that are preferable for plant growth.

Factors that influence soil formation

(a) The nature of the parent material

(b) The climate of the area

(d) Lengths of time that parent material are exposed to soil formation process.

(e) The topography of an area where this process takes place.

NB: the role of these factors summarized below.

H₂O from rain

HUMUS

VEGETATION

Decay though action of organism to form

Air

Determine type of vegetation

CLIMATE

SOIL

H₂O from Underground

Weathering (it cause)

PARENT MATERIAL

Weathering process

MINERAL PARTICLES

Broken to form

Direction of soil formation

I: NATURE OF PARENT MATERIAL

This is the factor that influence soil formation, as parent material is lower layer in soil profile that is the source of the soil.

The parent material broken to form mineral particles hence due to the factor of nature that parent rock is either weaker or strong

The weak rock is easy broken but strong one may take long time

II: THE CLIMATE OF AN AREA

These may facilitate more broken of rock as action of rainfall, wind, humidity, temperature, and pressure

Pressure-(constraction and constriction cause pilling away of rock surface material)

Temperature-(direct sunlight cause increase in temperature through rocks to cause break down)

Rainfall, wind, humidity – (cause breakdown due their action)

III: LIVING ORGANISM

The living organisms play part on:

(1) Formation of soil by decomposition of microorganism.

(2) Soil formed by plant roots through creaks.

(3) Vegetation that develops on the surface of the soil determine the x-tics of soil.

IV: TIME

Length of time of parent material: Long life parent material are easy to undergo weathering example, physical weathering. It can undergo breaks and peeled out as how long life it lives

Short live parent material on the surface of earth is difficult to undergo weathering.

V: TOPOGRAPHY

In topography we consider relief and drainage of a place.

The amounts of soil erosion depend on topography that is flatland, or sloping.

Undulating: the erosion of soil under mass wasting occurrence facilitate soil formation.

SOIL CATENA: Is the succession or series soil formed from issue parent material or parent materials that are similar in chemical composition and age in areas at similar climate but has different characteristics due to differences in topography.

NB: Effect at topography cause soil catenation Or soil associations

Example of such soil is Ukiriguru soil catena in Mwanza

Reddish sandy with grey concentrated subsoil

HILL

Course red

Sandy soil

Grey sandy (water table)

Black creaking clay

(Mbuga)

Itongo , kikungu , itirusi

Hogoro and Imbambasa

Lusenyi

2.1.3 WEATHERING

Weathering: Is the process of breaking down parent material or small particles in to vary smallest particles by physical, chemical and biological process.

TYPES OF WEATHERING

(1) Physical weathering

(2) Chemical weathering

(3) Biological weathering

I: PHYSICAL WEATHERING

This is the broking down of parent material and small particles by physical mean (Mechanical mean)

- The mechanical process are:-

(a) Exfoliation

This is a pilling up of upper surface of the rock by the action of rock pressure due to commodity and

(b) Disintegration

Is the broken down at rocks to small particles by action at tectonic forces from the ground or high temperature and pressure. at surface earth.

II: BIOLOGICAL WEATHERING

This is weathering by the action of living organism (Animal and Plants)

(a) Animals – activities such as mining.

– Overstocking of animals.

– Decomposition of microorganisms.

(b) Plants – movement at roots through rock cracks

– Decomposition of vegetation to case …

III: CHEMICAL WEATHERING

This due by the chemical process such as

(a) Hydrolysis: breaking down of rocks by the action of water.

Illustration: .

(b) Hydration: This is the removal of crystallized water from rock that cause cracks to that rock as the initial point form weathering.

It’s associated by change in color to reddish or orange colour. If oxidant does unit take place the colour remain bluish grey.

(d) Reduction: This is the decrease in oxidation number of Iron ( )

Example:

(e) Dissolution: This is the process where as Alkali earths (Soda, Potash lime and) are split to sodium as hydroxide action to soil water as bicarbonates.

Illustration

(f) Acidification: This is the cation where as from atmosphere react with rain water to form carbonic acid that cubines with potassium and calcium rocks to disintegrate that rocks.

Illustration:

2.2 SOIL AND ITS COMPONENTS

2.2.1 What is soil?

- Is the upper most part of the earth crust which supports plant growth?

COMPONENTS OF THE SOIL

1. Mineral matter 45%

2. Organic matter 5%

3. Water 25%

4. Air 25%

5. Living organic - variable

2.2.2 PHYSICAL PROPERTIES OF THE SOIL AND ITS COUSTITUENTS

1. Soil texture

- Is the relative proportion of different sized particle in a soil sample?

- It refers to the feel, coarseness or fineness of the soil.

- It is determined by relative proportions of sand, silt and clay.

- Soil particles are classified according to their diameters as shown below.

Diameter of particle in mm	Name of particle
Less than 0.002	Clay
0.002 – 0.02	Silt
0.02 – 0.2	Fine sand
0.2 – 2	Course sand
2 – 20	Fine gravel
20 – 200	Gravel

For each soil texture class name is given such as

(i) Sandy soils.

- Soil containing 70% or more sand.

(ii) Clay soil

- Soil containing more than 35% clay and less than 50% sand.

(iii) Loam

- Soil containing up to 50% sand less than 30% clay.

Loams are agriculturally the most important soil as they are ideal for the majority of agronomic crops.

PROPERTITIES OF SAND SOIL

(i) Well aerated, good drainage and easy to cultivate.

(ii) Have low water holding capacity and are poor almost all plant nutrients.

(iii) Particles are loose hence can easily be eroded.

PROPERTIES OF CLAY

(i) Poor aerated and drained.

(ii) High water retention and rich in plant nutrients.

(iii) When moistened expand and when they dry become hard and cracks.

(iv) They are difficult to cultivate.

DETERMINATION OF SOIL TEXTURE

The texture of the soil can be determined both in the field and in the laboratory.

IN THE FIELD

- The texture is commonly determined by the sense of fell.

- The soil is rubbed between the thumb and fingers preferably in the wet condition.

SAND: - Give a gritty feel.

SILT: When dry gives a feel of flour and are slightly plastic when wet.

CLAY: Have a plastic feel and exhibit stickiness when wet and hardness when dry

This method is not accurate.

IN THE LABORATORY

Particle size distribution – this is done by using sieve which gives the amount of sand, silt and clay separate.

NB: This also done by following ways

- Use of microscope

- Use of capillarity

- Decantation of muddy

- Triangle percentage

I: USE OF MICROSCOPE

This is the method were as a Sample soil taken under electron microscope for easy determination of soil texture

Ø Majority of clay minerals are formed as a result weathering, unlike sand and silt which are usually moved directly from the primary or original rock. Particles are very fine, rarely greater than 2mm. the majority of clay particles are usually much smaller than 2. Single clay particles are too small to see with the naked eye. Under the most powerful microscope they are difficult to see, because clay particles tend to hold neither in group. Most of the structure studies of minerals (see fig bellow) has been facilitated by photographing them under an electron microscope.

Soil particles under electron microscope

Clay particles are held very closely together and therefore clay soils contain less and are poorly drained. When wetted, clays do not feel gritty like sand but become sticky and easily molded. The clay particles are responsible for the physical and chemical characteristics of clays.

An Agronomist use microscope to determine soil texture

II:USE OF CAPILARITY

The proportion of the different size particles in a soil determines the texture of a soil. Soil texture refers to the percentage composition in a soil of sand, clay and silt particles.

Determination of soil particle through capillarity is simple and also is profitable because it also may determine soil properties such as soil aeration, drainage, nutrients, holding capacity as by all this is through the separation of soil particles by water in capillary tubes

See fig bellow

Determination of soil texture by capillarity

Sand soil: the water amount is low because of poor water holding capacity and high drainage with good aeration through large particles as seen on the capillary above

Clay soil; the amount of water is high because of it’s high holding capacity and poor drainage as why water high even capillary tube open at the top

Loam soil; things are moderates as it’s seen the water balances

III:.DECANTATION OF MUDDY

This method is done by placing sample soil in the bottle with clean water for a time until settlement of muddy occur (see the fig bellow)

A mixture of water with sample soil to form muddy, and on how it’s seems after several time

š The separation of soil seen clearly as it’s classified bellow, ;the decantation process consider duration percentages

š The classification done as follows as it’s seen clearly in the fig above

This process consider duration of time as you seen above sand soil is just 1 minutes but silt soil is up to 2 hour and above

IV.DETERMINAITON BY TRIANGLE PERCENTAGE

This method is by use of triangle percentage diagram as seen bellow, ;this method is more explained at the classification of soil texture bellow

A triangle percentage

THE SOIL TEXTURE CLASSIFICATION

A soil in which sand particles predominate shows a coarse texture while a soil in which clay particles predominate has a fine texture. Thus a soil may be termed gravelly, sandy, silty or clayey depending on the proportion of the particles in the soil. As different size particles have different physical properties, the proportion of them in a soil will therefore influence the soil properties; physical and chemical. For example, gravel particles are rather large and also heavy due to their high content of iron. Consequently gravelly soils contain large spaces between the particles and soils contain large spaces between the particles and these spaces allow water to drain off very quickly. Because of this gravelly soils have a very poor water-holding ability

They are also very poor in plant nutrients. By comparison, clay particles exhibit a large surface area and therefore have a considerably greater capacity for holding nutrients and water than either gravel or sand. On soil texture depends aeration, drainage, nutrient and water-holding capacity of the soil, penetrability by the roots, etc. Lastly, the ease of working or cultivating a soil will very much be influenced by its texture. Thus clay soils, having a fine texture, are described as heavy soils due to the difficulty encountered in working them. Sandy soils on the other hand are described as light soils, because they are relatively easy to work compared with clay types.

THERE ARE SEVERAL TEXTURAL SOIL CLASSES WHICH ARE NAMED AFTER THE SOIL PARTICLES WHOSE PROPERTIES CHARACTERIZE THE SOIL PROPERTIES. THE MAIN SOIL TEXTURAL CLASSES ARE:-

a) Sands

These are coarse-textured, well-drained and relatively low in plant nutrients. Sandy soils are usually acidic in reaction.

They contain 80-95% sand, 5 – 20% silt and clay and 0.1 – 1% organic matter. They contain only very small quantities of available water and may be deficient in calcium and magnesium. Improvement can be effected by adding the deficient nutrients and adding organic matter. These soils are also more prone to erosion than either clayey or loamy soils, mainly because sandy soils have a less stable structure on the surface.

b) Sandy loams

These are moderately coarse-textured, well- drained, moderately fertile and moderately to slightly acid. They contain 50 – 80% sand, 20 – 50% silt and clay and 0.1 – 3% organic matter. They have a moderately high water-holding capacity. Sandy loams may be improved in the same ways as sands.

c) Silty loams

These are fine-textured, fairly well-drained, fertile and slightly acid soils. They contain 20 – 30% sand, 70 – 80% silt and clay 0.1 – 4% organic matter. They hold enough water and plant nutrients e.g. nitrates. It is not very easy to maintain soil tilth in these types of soils. Potential for crop production can be improved by improving drainage and aeration.

d) Loams

These are moderately fine-textured, moderately well-drained, moderately fertile and moderately to slight acid. They contain 30 – 50% sand, 50 – 70% silt and clay and 0.1 – 4% organic matter. Loamy soils show good proportions of sand and clay in their composition. Consequently loamy soils are the best for crop production available.

e) Clay loams

These are very fine-textured, poorly-drained and from slightly acidic to slightly alkaline. They contain 20-50% sand, 20 – 60% silt, 20 – 30% clay and 0.1 – 6% organic matter. Clay loams hold large amounts of water and potential nitrogen. It is difficult to maintain tilth in this type of soil. Crop production is improved by drainage.

IMPORTANCE OF SOIL TEXTURE

(i) Relative resistance to root penetration

· Soil with high silt and clay contents usually retard root growth and its extent of branching.

· Plant growths in region with such soil are likely to carry poor vegetation if long dry seasons prevail.

· Root penetration is best where the surface is loose textured.

(ii) Infiltration of water

- Rain falling on a course textured soil enters the soil readly and little is lost in runoff infiltration rates for water entering heavy soils are low and run-off is high.

(iii) Rate of water movement

- The rate of water movement in the soil varies inversely with the fineness of soil texture.

Fine texture soil offer considerable resistance to the mass movement of water.

(iv) Soil fertility

Many of the nutrients ions which plants must extract from soil are adsorbed by the colloids. Colloids are particles with smallest size. Therefore, the finer the texture of a soil the greater is its fertility.

SOIL STRUCTURE

The soil separate do not exist independently as single grain, instead, they are bound together in clusters called AGGREGATES

- The smallest aggregate are called ped

- The soil separate and ped may further coalesce to form bigger aggregates of definite shape which constitute SOIL STRUCTURE

A soil aggregates in soil profile

Def. Soil structure is the arrangement of individual soil particle within the soil.

SOIL STRUCTURE IS DESCRIBED UNDER THREE CATEGORIES

(i) Soil structure type

(ii) Soil structural classes

(iii) Soil structural grades

SOIL STRUCTURE TYPE

- Soil structure type is described on the basis of the shape and arrangement of the peds.

(i) Plate line – the aggregates have more developed horizontal than vertical dimension giving a flattened or lens – like appearance.

a) Platy, with thick units.

b) Laminar, with thin units.

(ii) Prism-like the vertical axis is more developed than the horizontal one, with flattened side giving a pillar-like shape.

- This is commonly found in sub soil horizon of arid and semi arid regions.

- The aggregate may have two structures depending on the shape of the top.

(iii) Block-like

All the three dimensions of aggregate are of equal size and the aggregate resemble a block or cube. This type of aggregate is common in heavy soil sub-humid regions. The aggregate may have two structures depending on the shape of edge and faces.

(a) Granular-block, with sharp edges and distinctly rectangular face.

(b) Sub angular- blocky, with rounded face and edges.

(iv) Sphere-like these aggregates are nearly round.

- They are usually loose.

- These sphere – like aggregates are characteristics of many surface soil, especially in those high in organic matter.

- They may have two types of structure depending upon the porosity of the aggregate

a) Granular-non porous

b) Crumby - porous

SOIL STRUCTURE CLASSES

Soil aggregate can be grouped on the basis of size into structural namely:-

i. Very fine or very thin.

ii. Fine or thin.

iii. Medium.

iv. Course or thick.

v. Very course or very thick.

SOIL STRUCTURAL GRADE

Various soil structural grades are recognized on the basis of degree of distinction and stability of individual aggregates.

- The grades are determined by performing an aggregate stability analysis and the ease with which these aggregate separate from one another.

- Four grade of structure designed from 0. to 3.0 structures: in this grade there are no noticeable aggregate e.g. loose sand or cement like condition of same clay soil.

- If the appearance is Coherent as in compact clay, the structure is termed as massive.

- If non-coherent as in loose sand the structure is termed as single grain.

1. Weak

Aggregates are poorly formed.

2. Moderate

Aggregate are well formed.

3. Strong

The aggregate are quite evident and durable in undisturbed soil.

NB: refer the concept of soil profile at the introduction

GENESIS OF SOIL STRUCTURE

- This refers to the cause and methods of formation of structural units or aggregate.

- Generally aggregate formation is due to cementation of soil separates and peds.

- Also disintegration of bigger aggregates into smaller one result in the formation of soil structure.

(i) Adsorbed cations

- The positively charged particles held on exchange site of colloidal practical are called adsorbed cations.

These have a property of flocculating and dispersing the soil particles.

Example: calcium flocculates the soil colloids while organic matter may cement the floccules to form aggregates.

- Sodium ions disperse the soil separate.

The role of cation in aggregate formation is believed to be associated with the orientation of water molecules.

Water molecule being dipolar orientate along the negatively charged colloidal particles.

Cation acts as a bridge between two colloidal particles having a chain of dipolar water molecules.

When water evaporates, the lengths of chain molecule decrease and bring the colloidal particles together to form aggregate.

2. Clay

They clay fractions in the soil play an important role in aggregate formation.

Clay particles coalesce themselves due to force of attraction (cohesion)

- They also act as cementing agents in binding sand and silt.

3. Organic Matter

- Organic matter is the major cementing agent in the formation of granular aggregates in surface soil, especially in soil of low clay content.

- Plant root promote aggregation during their growth thought mechanical compression and root secretions.

4. Climate

- With increasing rainfall chemical weathering is intensified. This result in formation of more clay colloids and hence more aggregates.

- High rainfall also favours vegetation and accumulation of organic matter in the soil.

- High temperature enhance organic matter decomposition and therefore its decrease in the soil.

- High temperature may also favor aggregation through dehydration.

5. Alternate wetting and drying

- Dehydration of soil colloids causes shrinkage of soil mass and cementation of clay particles.

- During wetting, rapid intake of water cause swelling throughout the soil clod. This renders fragmentation along the cleavage plane.

6. Tillage practices

- Tillage has both favorable and unfavorable effects on granulation.

- A short term effect is often favorable because implements loosen the oil and mix organic matter with it.

- Continous tillage operations have detrimental effects on soil structure. In addition heavy implements tend to break down the stable soil aggregates.

7. Cropping

Crops with a good ground cover reduce the deterioration of soil structure as the impact of rain drops on surface soil is minimized leaves and stems.

- In addition, plant roots help in granulation.

8. Soil amendments

- The addition of manure, fertilizer and lime has favorable effect on granulation through the enhancement of root and shoot growth and microbial activity.

IMPORTANCE OF SOIL STRUCTURE

Soil structure influences almost all plant growth factors such as:-

(1) Water supply.

(2) Aeration.

(3) Availability of plant nutrients.

(4) Microbial activity.

(5) Seed emergence and

(6) Root penetration.

SOIL DENSITY

- Is the weight per unit volume of soil.

- Physical properties of the soil are determined by the composition and stability of soil separates and peds, their volume and weight.

- Their relationship with soil organic matter is particular significance in agriculture and engineering. For instance, fine textured soils have more weight per unit volume than course textured ones.

- The addition of organic matter to either of the soil texture classes will reduce their densities but increase porosity.

- The density of the soil can be expressed as

(i) Particle density (true density)

(ii) Bulk density (apparent density)

PARTICLES DENSITY

- It is defined as weight per unit volume of soil solid.

PD = weight of soil solid

Volume of soil solids

- The spaces between solid matters in the soil mass are called PORE SPACE. These are filled with air and water.

- The particles density is related to solid portion of the soil mass only.

- In general mineral soil have a particle density that varies between 2.6 and 2.75 g/cc.

- The value of PD decrease with increasing organic matter weight less than mineral solids.

- This means that the amount of organic matter presents in the soil determine the PD of the soil, the higher the quantity of organic matter in the lower the PD and vice versa.

- Therefore, surface soil have lower particle density than sub-soils.

BULK DENSITY

This refers to weight of dry soil per unit bulk volume including the air space.

BD = weight dry soil

Bulk volume including air space

FACTOR THAT AFFECTING THE BULK DENSITY OF THE SOIL

(1) Organic matter content – organic matter is light and therefore lowers the weight of the soil. As such if it is presents, in the soil, it also lowers the bulk density.

(2) Granulation – A soil that is well granulated has s lower bulk density than one which is not well granulated.

(3) Compactness of the soil – A compact soil has very little pore space. As a result it has a high bulk density.

(4) Cultural practices – Continous cultivation without addition of organic matter tends to raise the BD while addition of organic matter lowers the BD.

SOIL POROSITRY

- Is the sum total of space not occupied by soil solid in a soil mass. These spaces are usually filled with water and air.

- There are two types of space basing on their size.

(1) Macro pore (non-capillary) – bigger in size and allow free water and air movement.

(2) Micro pore (capillary pore) – small in size and air and water in such pores is considerably impeded due to two capillary movement of water.

Percentage pore space is expressed as; percentage pore space = 100 x (1-BD)

%PS = 100 – BD X100

FACTS ON POROSITY

1. Sand soils have large pores but the total porosity is small due to the large particle density.

2. Fine textured soils have high porosity due to their high bulk density.

3. Presences of organic matter in the soil increase porosity of the soil because it encourages granulation.

4. A soil that is compact has less total pore space than one that is loose.

SOIL AIR

- Is the percentage of gaseous components of soil which occupies the pore space not filled by water.

- It is important for plants and soil inhabitants.

- It is required for root respiration in higher plants as well microbial activities.

COMPOSITION SOIL AIR

v Oxygen 20.55%

v Carbon dioxide 0.25%

v Nitrogen and others 79.2%

FACTORS AFFECTING COMPOSITION OF SOIL AIR

1. Soil physical properties

- Texture, structure, organic matter and moisture content affect soil air because they affect air capacity and permeability in a soil.

2. Agronomic activities

Presence of growing plants tends to reduce oxygen (0₂) content of soil and increase carbon dioxide (C0₂) due to root respiration.

3. Biological activities

Decomposition of organic matter utilizes oxygen (0₂) and evolve carbon dioxide (C0₂) hence change the composition of soil air.

4. Seasonal variation

Variation in temperature and moisture cause fluctuation in composition of soil air, as water increase, amount of air in soil is reduced.

Questions

1. When a sample of soil was analyze in the laboratory, the following information was recorder.

v Weight of wet soil 280gm

v Volume of soil solid 220cm³

v Weight of oven dry soil 220gm

v Volume of pore space 25cm³

Calculate;

(i) Bulk density

(ii) Particle density

(iii) Percentage pore space.

Solution

(i) Bulk density (BD) = weight of dry soil

(ii) Particle density

(iii) Percentage pore space.

Solution:

(i) Bulk density (BD) = Weight of dry soil

Volume of soil + volume of air space

BD = 220

220 + 25

= 0.897g/cm³

(ii) PD = weight of the soil solid

Volume of soil solid

= 220gm

220cm³

PD = 1g/cm³

(iii) % PS = 100 (1 -BD)

= 100(1-0.897g/cm³)

1g/cm³

= (1-0.897)100

% PS = 10.3%

IMPORTANCE OF SOIL AIR

1. Oxygen is required for root respiration and soil organism.

2. Carbon dioxide help to dissolve nutrients from rock and minerals.

C0₂ + H₂0 H₂C0₃ (Weak acid)

3. Nitrogen of soil air increase soil fertility.

4. Water vapor prevents the desiccation of roots and microbes.

MANAGEMENT OF SOIL AIR

1. Improve soil structure

2. Maintain adequate amount of soil moisture.

3. Increase soil temperature to accelerate diffusion.

4. Improve soil porosity

5. Adjustment of plant density (plant crops with oxygen requirement) avoids heavy feeder crops.

SOIL COLOUR

- These are different colours that occur in the soil.

- Soil color has no direct effect in plant growth but it has an indirect one through its effect on temperature and moisture.

- Soil color can be indicator of climatic condition under which a soil was developed or of its parent material.

- The productivity of the soil can be guessed from its colour

COLORS THAT OCCUR IN THE SOIL

All colors except pure blue and green occur in the soil. These includes

v White

v Red

v Brown

v Grey

v Yellow

v Black

Predominant colors are grey, brown and rust.

CAUSES OF SOIL COLOR

1. Presence of soil composition colloids.

a) Humus –dark brown or black

b) Iron oxide –yellow, red or brown

c) Quartz (S₁0₂) – Grey or white

d) Clay – white, grey, black red

e) Limestone (CaCo₃) – white or grey

f) Moisture content

- The more moist is the soil the darker is the color due to refractive property

SIGNFICANCE OF SOIL COLOR

1. To know soil productivity

- Black/dark: indicate high productivity

- While soil: indicate poor fertility

2. In young soil, light color is an indication of the parent material, while in mature soil it is an indication of the climate in which the soils have developed.

3. Help in classification of soil. Example: charnozem (black), sierozem (grey), krasnozem (red), pod sol (ash grey).

4. Help to study soil profile description

5. Soil color influence other soil properties. Example: dark soil is warm than light soil.

SOIL TEMPERATURE

Soil temperature is the degree of hottest and coldness of the soil

- An equipment used to measure soil temperature is soil thermometer.

IMPORTANCE OF SOIL TEMPERATURE

1. Increase seed germination.

2. Help to increase number and activities of micro-organism.

Example:

v Psychrophiles – cold lovers micro – organism

v Mesophiles: medium temperature micro – organism 20⁰C -30⁰C

v Thermopiles: high temperature lovers 80⁰C

3. Improves soil color properties.

FACTORS AFFECTING SOIL TEMPERATURE

(I) Solar radiation – Increase soil temperature.

(II) Condition of heat from the atmosphere. Air convection or wind is necessary in the heating up of the soil by conduction from the atmosphere.

(III) Condensation and evaporation.

- Condensation is exothermic process. When water vapors from the atmosphere or from other soil depths condense in the soil, it heats up noticeably. Under such condition increase in 5⁰C have been noted.

- Evaporation, the more the soil is cooled down.

(IV) Rainfall

Depending on its temperature, rainfall can cool or warm the soil.

(V) Insulation

The soil can be insulated from environmental temperature by plant cover, mulch, snow. clouds etc. insulation serves to maintain soil temperature.

(VI) Vegetation

Plant cover saves as insulator

(VII) Thermal capacity

Example: Organic matters have high thermal capacity than mineral matter.

(VIII) Microbial activities- micro – organism activities in the soil evolve heat.

(IX) Moisture content of soil – e.g. irrigation can alter moisture content of the soil.

MANAGEMENT OF SOIL TEMPERATURE

a) Mulching – keep the soil hot.

b) Planting vegetation – can keep the soil cold.

c) Irrigation by warm water, increase soil temperature.

SOIL WATER

Is the percentage of moisture which occupies the micro and macro pores of soil and consist of about 25% by volume.

FUNCTION OF WATER IN SOIL

1. Influence weathering and erosion which lead soil formation.

2. Is a solvent and act as carrier of plant nutrients.

3. Needed to maintain turgidity and body temperature of plants.

4. Is essential in photosynthesis and other plant metabolic activities.

TERMS USED IN SOIL WATER

(1) Infiltration – Is the downward entry of water in the soil.

(2) Permeability – Ability of gases, liquid or plant roots to penetrate through a bulk of soil or rock.

(3) Percolation – Is the downward movement of water through column of soil.

(4) Retention of water – Is the abundant accumulation of water due to holding capacity of soil.

(5) Soil moisture constant – Is the phenomena of amount of water held in the soil at various tension. This enable us to understand the amount of water that is available to plants.

- As soil moisture content increase water tension decrease (available water to plant decrease)

Two forces largely account for the retention of moisture by soil colloidal surface.

(i) Adhesion – Attraction of the colloidal particles for water molecule.

(ii) Cohesion – Attraction of water molecules for each other.

The size pore space and their distribution in the soil and the attraction of soil solids for moisture determine to a large extent the movement of water in the soil and the ability of that soil to hold water.

- When there is plenty of water in the soil, the water is held by the solids with very little suction or tension.

- Some is held so weakly that it flows away down the slope or downwards deep in the soil profile so that it is lost.

- As the amount of water remaining in the soil become smaller, the remaining water becomes held even more strongly by the soil.

- The suction with which water is held in the soil is normally expressed in term of atmosphere.

Assume this soil particles is surrounded by a film of water as shown.

Relationship between thickness of water film and tension.

2.2.3 SOIL MOISTURE CONSTANTS

The knowledge of the amount of water held by the soil at various tensions is required for the calculation of the amount of water that is available to plants.

1. Saturation

A soil whose pores are completely filled with water is said to be saturated.

- This implies that the water in the soil is at zero tension.

2. Field capacity

Field capacity can be defined as the amount of water held in the soil after the excess gravitational water has drained away and after the rate of downward movement of water has ceased.

- It is held at tension of 1/3 atmosphere.

3. Wilting point or wilting coefficient

Wilting point refers to that soil moisture content at which soil fails to supply water at a sufficient rate maintain turgid, and the plant permanently wilts.

- Is the amount of moisture remaining in a soil when soil reaches a point where its moisture content is similar to that of a soil which has been oven dried (105⁰C). At this point plants fail to absorb moisture and therefore wilt.

4. Hydroscopic coefficient/point

- Is the point at which water is held at a tension of 30 atm where by at this tension water is not available to plants but may be available to a certain micro-organism

5. Oven dry

- Soil is considered to be oven dry when it has reached equilibrium with the vapor pressure of an oven at 105⁰C.

- The equilibrium tension of moisture at oven dry is 10,000 atmospheres.

MP% = Air dry weight – Oven dry weight x 100

Oven dry weight

Where as: MP = moisture percentage

2.2.4 SOIL WATER CLASSIFICATION

Soil water may be classified on the basis of physical biological properties.

Physical classification

- This is based on relative degree of retention.

(i) Free or gravitational water- this is the water which enters into the soil and passes out through soil by gravity.

- Water which is in excess of field capacity.

(ii) Capillary water – water held between the field capacity and hydroscopic coefficient.

- This water is not available to plant.

(iii) Hydroscopic water is held at the hydroscopic coefficient at tension varying from 31-10,000 atm.

- This water largely non-liquid and moves in the vapor phase.

(iv) Water of crystallization – is that type of water which is part of crystal structure and it is not available to plant.

(v) Water vapor – exists in gaseous phase.

BIOLOGICAL CLASSIFICATION

This is based on the extent of utility by plants.

(i) Superfluous water – Is the one which is excess of that held at field capacity.

(ii) Available water- is that water which is held between the field capacity and wilting coefficient.

- This water is useful for plant growth.

(iii) Unavailable water – Is the water which is held in the soil that soil is at the wilting point. It cannot be absorbed by plant root, hence plants wilts.

2:3 SOIL CHEMISTRY

2.3.1 SOIL COLLOIDS

- Are organic and inorganic matter with extremely small particles size, usually in range of 10A (one angstrom unit = 10 cm).

- The term colloid originated from the Greek world’s kola, which means glue and aides which means form.

- A colloid is a substance which when apparently dissolved cannot pass through membrane.

- A simple suspension is a two phase system.

- The phases are distinguished by two terms.

(i) Dispersed phase – this is the phase forming the particle.

(ii) Dispersion phase – this is the medium in which the particles are distributed.

Therefore the particles forming dispersed phase are termed as colloidal.

- Any substance under suitable conditions may be sub-divided to yield colloidal particles and the substance is then said to be in a colloidal state.

SOIL COLLOIDS

- The colloidal particle in a soil is the seat of chemical activities.

- There are two types of colloidal particles.

i) Organic colloids – This includes humus particles.

ii) Inorganic or mineral colloids – Are exclusively clay minerals and oxides of iron and aluminium.

Fig: a soil colloids in soil solution

PROPERTIES OF COLLOIDAL PARTICLES

1. Surface areas

ØThe colloidal particles being small in size expose enormous surface area for chemical reactions and water retention.

2. Electric charge and ion exchange

Ø The colloidal particles carry net positive or negative charges, hence high capacity to hold and exchange ions on their surface.

3. Flocculation

Ø In the field of chemistry, is the process in which colloids come out of suspension in the form of flock or flake, either by spontaneously or due to addition of clarifying agents.

Ø Flocculants or flocculating agents: are chemicals that promote flocculation by causing colloids and other suspended particles in liquids to aggregates forming a flock. Flocculants are used in water treatment processes to improve the sedimentation or filterability of small particles

Patch flocculation formation

4. Tyndall effect

Ø The individual colloidal particles in a colloidal dispersion can be demonstrated by passing a strong beam of light through it due to their property of scattering light.

Ø This property in known as the Tyndall effect after it’s discover.

Ø A beam of sunlight in often visible from the side in a room passing through any orifice because the light is scattered by dust particles.

5. Brownian movement

The colloidal particles in dispersion are always in a random motion. The motion of individual particles continuously changes direction as a result of random collision with the molecules of dispersion medium, other particles and the wall of the container.

- Each particles purposes a complicated and irregular zigzag path. This random motion is referred as Brownian movement after the botanist Robert brown who first observed this phenomenon with pollen grain suspended in water.

6. Dialysis

The process of separating colloidal particles from dissolved salt through semi-permeable membrane is termed as Dialysis.

The membranes retain the colloidal particles during dialysis while salt and other impurities dialise out.

7. Plasticity

- Colloidal particles exhibit property of plasticity i.e. capacity of being molded without breaking.

8. Cohesion

- Attraction of particles for each other.

9. Swelling, shrinking and cracking

Colloidal particles swell upon wetting and they shrink and crack upon drying.

ION EXCHANGE

Def.: is a simple reversible process in a colloidal system in which an ion replaces another with charge of the same sign.

The presence of electric charge on the surface makes the colloidal particles capable of holding ions.

These ions in turn can be exchanged by others in the soil solution surrounding the particles.

This means that an ion in the vicinity of the colloidal particles may replace another on its surface.

Ion exchange takes place between liquid phase and solid or between closely lying solid particles such as two clay or humus and plant root.

Ion exchange between two solid particles does not need water or solution phase and is known as contact ion exchange.

- The net electric charge carried by colloid particles may be positive or negative.

- The negatively charged particles hold cations, which are exchangeable with those in the vicinity. This is known as CATION EXCHANGE

WHAT IS CATION EXCHANGE?

- Is the exchange of cations, the positively charged ions between one medium and another.

Cation exchange

CONTACT CATION EXCHANGE

Cation exchange is the interchange of cations in soil solution that one on colloids must be charge balanced thus we mean must replaced be three another ions to replace charge

3K =

This three potassium is replaced by alluminium in soil solution

And if we say contact cation exchange we mean exchange of cation without water (without soil solution),so it replace each other as you see there at fig, above

The positively charged particle can hold and exchange anions, the process being known as anion exchange.

What is anion exchange?

Is the exchange of anion, the negatively charged particles between one medium and another

ANION EXCHANGE

Anion exchange

Contact anion exchange

Anions is held by cation and cause anion exchange ,so anion exchange is carried by presence of cations

2.3.2: SOIL CALCULATION

Cation exchange capacity

This is defined as sum total of exchangeable cations held in a soil, and it is expressed as mill equivalent (m.e) per 100g of dry soil.

Soils high in organic matter have higher C.E.C than those low in organic matters.

PERCENTAGE BASE SATURATION

Among various cations neutralizing the negatively charged sites, hydrogen and Aluminium are related to the soil acidity.

Cations other than Aluminium and hydrogen constitute the base saturation of the soil.

It is expressed as:-

PBS =

C.E.C

WHERE

· EB = (Exchangeable cations) – (exchangeable ( ).

· C.E.C = Total cation exchange capacity.

- The base saturation of normal cultivated soil is higher in arid than in humid regions.

- The PBS has s definite relationship with the PH and the fertility of soil.

- The higher the percentage base saturations the greater is the availability of basic cations to plants, although is controlled by the nature of the soil colloids.

- Clay minerals 2:1 type (40-80 me/100g) have higher C.E.C than 1:1 (10-20me/100g).

SOIL COLLOIDS AND AVAILABILITY OF NUTRIENTS TO PLANT

- The exchangeable ions held on the colloidal surface are generally readily available to plants.

- The amount and type of colloidal particles has an influence on the availability of nutrients elements to plant.

- The higher the amount soil colloids, the greater is the C.E.C

- But the availability of cations will depend on the type of soil colloids because the colloids differ in their affinity to hold specific cations.

EXAMPLE:-

Montmorillonite holds calcium more tenaciously tan kaolinite. For that case higher degree of calcium saturation is required before it is readily available to plant in montmorillonite than in kaolinite.

- Soil colloids especially 1:1 clay and hydrous oxide of iron and aluminum commonly found in tropical soil have a large capacity of fixing phosphate, thus availability of this nutrients is slowed down or stopped for longtime in such soil.

- Since soil colloids have the property of ion exchange the nutrients (cations) such as added through fertilizers are held on colloidal surface and thus served from leaching.

WORKING EXAMPLES

Example 1

A soil sample was collected from a certain farm for laboratory analysis. After being analyzed soil had the following exchangeable cations.

Ca = 30 me/100g

Mg = 16me/100g

K = 5me/100g

H = 4me/100g

How many milligrams of these elements in the soil and what is PBS of thesample

Solution

Equivalent weight = Molecular weight

Valency

Mill equivalent = millgrams

Equivalent weight

Equiv. wt = molecular wt

Valency

^40/2 = 20

Mill equivalent = mg

Equv. Wt

30= mg

= 600mg

Find mg, K and H.

%BS =

C.E.C

%BS = E.C – (

C.E.C

= (30 + 16 + 4) - 4 100

= 51

% BS = 92.75%

Example 2: A soil sample of 20g was analyzed and found to contain 0.0015 of . What is the concentration of calcium in the soil.

Solution

Calculate the equivalent wt of calcium

Equiv. wt = molecular wt

Valency

40/2 = 20g

1 equiv. wt of = 20g

100 me = 20g

I me = ?

20x1 = 0.02g

1000

I me = 0.02g

Therefore;

I m.e = 0.02g

X = 0.0015g

1x0.0015 = 0.075 m.e

0.02

If 20g _________ 0.075 m.e

100g __________ x

100gx0.075 m.e

20g

= 0.375 m.e

Concentration of = 0.375 m.e/100g of dry soil.

EXMPLE 3:

A soil sample has a cation exchange capacity of 25me/100g; 20g of soil were shaken with of 0.1 Hcl,

After filtering and washing the soil, the filtrate and washing were titrated against NaOH solution. 24cm³ of 0.1M NaOH were required to complete neutralization. Calculate the PBS.

Solution:

Data

C.E.C = 25 m.e/100g

PBS = To be calculated

to be calculated

neutralize

___________

0.1m of =

1000

Moles of base used

0.1M =

1000

Therefore;

0.0024 moles of 0H^- neutralize 0.004 moles of H⁺ leaving 0.004 – 0.0024 = 0.0016 moles of H⁺ which neutralize the soil bases.

Therefore

0.0016M of H⁺ = 0.0016g of H⁺

Since 1 equiv. wt = 1g of H⁺

Therefore;

1 equiv. = 1g of H⁺

100 m.e = 1g of H⁺

X = 0.0016g of H⁺

1000 x 0.0016

= 1.6 m.e

Therefore:

20g of soil = 1.6 m.e

100g of soil = x

100g x 1.6 = 8m.e

20g

PBS = 8/25 x 100 = 32%

Example 4:

If a soil has PBS of 60% containing 8m.e of exchangeable hydrogen per 100g of dry soil. Calculate C.E.C.

Solution

PBS = = C.E.C – Exchangeable (H⁺ or Al3⁺)

Therefore

60% = (C.E.C – 8) X 100

C.E.C

60 = C.E.C -8

100 C.E.C

0.6 C.E.C =( C.E.C – 8)

C.E.C=8/0.4

C.E.C=20

Example 6:

A certain soil contains the following cations, where all valuesare gigen in Meq per 100 grams of oven dried soil.

Mg²⁺ = 20, Ca²⁺ = 38, Na⁺ = 4, K⁺ = 6, mn²⁺=2, H⁺= 24 and Al³⁺= 8

If the cation exchange capacity of the soil is 96 Meq in 100g of oven dried soil, calculate

(i) Percentage base saturation of this soil.

(ii) Quantity of calcium in gram present in 100g of oven – dried soil.

Note: 1g = 1000mg.

2.3.3: SOIL REACTIONS

Definition

Is the condition of the soil solution which in expressed in terms Ph.

Is the measure of alkalinity or acidity of the soil and which is expressed as Ph.

The soil solution (the liquid phase in a soil) may be acidic, neutral or alkaline in reaction.

The main factors that determine the reaction of the soil is the concentration of H⁺ and OH⁺which are present in the soil solution.

- When there is more H⁺ than OH^- in the soil solution the soil is said to be ACIDIC and the vice versa the soil is said to be ALKALINE.

Soil with an equal concentration of H⁺and OH^- are neutral in reaction.

Therefore, soil solution may be acidic, neutral or alkaline in reaction.

What is soil Ph?

- Is the negative logarithm of hydrogen ions concentration of the soil solution.

§ The PH scale run from 1 – 14.

§ Ph 7 – neutral

§ Below 7 – Acidic

§ Above 7 – Alkaline.

§ Although the Ph scales run from 1 – 14 most soil, however have a Ph lying between 3.5 and 11.

§ This range in soil Ph is usually translated as:-

Ph range description

3.5 – 4 ……………………………. Very strong acid

4 – 5 ……………………………… strong acid

5 – 6 ……………………………… moderate acid

6-6.9 ……………………………… slightly acid

7 ………………………………….. Neutral

7.1-8 ……………………………… slightly alkaline

8.0-9 ……………………………… moderation alkaline

9-10 ……………………………… strongly alkaline

10-11 …………………………….. Very strong alkaline

METHODS OF DETERMINING SOIL Ph

Two methods are used

1. The electrometric methods

2. The colorimetric methods

THE ELECTROMETRIC METHOD

In this method the PH is determined by means of PH meter.

- When using a PH mater the H+ concentration of soil solution is balanced against standard hydrogen electrode. A reading of PH is then made. This method is more accurate than colorimetric method.

How:

- The PH meter is plugged into soil and a needle will jump into approximate Ph reading for your soil.

THE COLORIMETRIC METHODS

In the colorimetric methods dyes which develop differ colors at different Ph value are used Kits for use in the laboratory are available.

PROCEDURE:-

Fill a small test tube that comes with soil test kit about quarter full soil, and then add colouring agents and fill with distilled water, shake the mixture until water turns color.

For example:

A deep green colour shows that the Ph is rouns 8.

The soil test kit contain necessary chemical and color chart.

SIGNIFICANCE OF SOIL PH

1. The suitability of a soil as a medium for the growth of plants and micro-organism depend on PH.

- The favourable range for the majority of crops is from slightly acidic to slightly alkaline

(6-6.9) – (7.1 – 8.0) Ph.

- But acidic PH is sometimes desired for controlling disease e.g. potato scab. Also a crop like tea required acidic soil conditions.

2. Soil Ph affect the availability of nutrients elements to plant.

Example:-

Nitrogen, phosphorus, potassium, calcium and magnesium are available in Ph range of 6.5-7.5

- Acidic Ph increase the availability of iron, manganese, copper, chlorine and zinc but reduce that of molybdenum

3. Soil Ph affects the activity of micro-organism.

- Organic matter decomposition slow down under extreme acidity or alkaline soil condition due to decreased microbial activity.

4. SOIL Ph determines the amount of amendments needed (for liming or acidification) to bring favourable soil condition for plant growth and microbal activities.

5. Soil Ph help in the selection of suitable crop to be grown in a certain piece of land. This is because crops vary in their tolerance to acidity or alkalinity.

TYPES OF SOIL ACIDITY

Soil acidity may be defined as

- This is a soil whose hydrogen ions (H⁺) are dominant in the soil solution.

There are two types of soil acidity

1. Active acidity – is the type of acidity in which hydrogen ions (H⁺) are in the soil solution.

2. Potential acidity (reserve) – is the type of acidity in which H⁺ are held on colloidal surface.

- When the concentration of H⁺ in the soil solution is diluted by rain or irrigation water, more H⁺ moves from the soil surface to the soil solution in order to maintain equilibrium.

- The reverse occur when H⁺ are released in the soil from decomposing organic matter or acidic- forming fertilizers.

- A potential acidity may also be due to the presence of Al³⁺ on the colloidal exchange site. The adsorbed alumunium is in equilibrium with Al³⁺ ions the soil solution.

CAUSES OF SOIL ACIDITY

1. Heavy rain or irrigation – this may cause the soil to be acidic due to the leaching of the bases e.g. Ca, mg, K, and Na.

2. Carbon dioxide evolved during root respiration and microbial activities forms carbonic acid.

3. Presence of small amount of anion such as No₃^-, H₂PO₄^2-, SO₄^2- and Cl^- contribute to soil acidity.

4. Application of acidic forming fertilizers such as ammonium sulphate (SA) and ammonium chloride.

5. Some acids

6. Are also produced during decomposition of soil organic matter.

Harmful effects of soil acidity

1. Cause harm to root.

2. Depress the availability of essential nutrient elements such as photosphorus, potassium, calcium and magnesium.

3. Increase solubility of iron, Aluminum and manganese to toxic level.

4. Depress the activities of micro-organism.

Management of acid soil

There are two problems of opposite nature which are encountered in the management of acid soil.

These are:-

I. Intensification of acidity.

II. Neutralization of the acidity

Soil fertility and its maintenance

What is a fertile soil?

Is the one that supplies all the plant nutrients and air in sufficient and balanced quantities.

The productivity of the soil is its ability to produce a specified amount or sequences of plant products under specified management conditions.

Ø The growth limiting factors must be adequately controlled in order to obtain the desired optimum productivity from a soil of particular fertility status.

Ø Some bad conditions which will reduce a soil productivity

i. Compaction.

ii. Improper drainage.

iii. Inadequate moisture.

iv. High salt concentration.

v. Acidic soil condition.

vi. Loss of crop soil through erosion.

The fertility of soil in any place depends on the following

1. Texture of soil.

2. Depth of soil profile.

3. Structure of the soil.

4. Chemical composition of parent rock.

5. Climate of the area.

6. Soil reaction.

7. Organic matter.

Soil texture bears importantly on soil fertility due to its influences on water and nutrient retention capacity and aerations.

Example:

Sandy soil offer good aeration but poor anchorage as well as poor water and nutrient retention while the opposite is true for clay soil.

Depth of the soil profile

- The depth of the soil profile determines the extent of root development. Deep soil increases the volume through which the roots can spreads and they have greater water and plant nutrients supply potential.

- Shallow soil duffer drought quicker than deep soils and they may limit the growth of many kinds of crops plant.

Composition of parent materials

- The compositions of parent materials influence the natural supplies of inorganic nutrients element and the ability of the soil to return them.

- This is particularly important for the element like potassium, calcium and magnesium all of which are obtained from inorganic source or combinations.

- The release of nutrients element into available forms depends on the rate of weathering.

Soil reaction

Soil reaction has an effect on nutrient available and hence soil fertility. The optimum Ph range suitable for most agricultural crops is 5.5 – 7.5, with an optimum around Ph 6.5.

At lower Ph range problem of impaired nutrition due to excess of free aluminum, manganese and iron in the soil may rise while at the higher Ph range some nutrients deficiencies may occur.

2.4: FERTILIZER AND MANURE

2.4.1 ORGANIC MATTER

- Organic matter acts as soil conditioner by improving structure, aeration and moisture and ion retention, besides being an important source of some nutrients elements.

Soil structure

Soil structure affects temperature, moisture status and aeration in soils. Structure can be altered by physical and chemical manipulation e.g. by cultivation, manuring and liming.

Loss of soil fertility

The soil loses fertility in several ways. The most important of these are

(i) Erosion

- When erosion occurs, soil is carried away either by wind or by water from one place to another place. During this process, the top soil is taken away.

- Since the top soil is most fertile, it means that when erosion occurs the remaining soil become less fertile.

Water Logging

Water logging occurs when all the pores space in the soil becomes filled up with water. As a result, almost all the air is driven out of the soil. Plants fail to grow properly because their roots do not get enough oxygen; they remain short and become yellow. If this continues, they finally die.

Leaching

Leaching is the process whereby nutrients is dissolved and are then carried downwards in the soil profiles away from plant root zone. When this happen, the roots cannot absorb nutrients.

Burning

When vegetation growing on the surface of the soil is burned, organic matter is destroyed and the ground is exposed because the protective layer of vegetation is lost. Also the organic carbon, nitrogen, phosphorus and sulphur which are present in the vegetation are destroyed.

Weeds:

Weeds absorb nutrients from the soil just as the crop plant do.

When these weeds are uprooted and are taken away from the field, the nutrients which they had absorbed from the soil are lost as well.

Harvesting crops

When crops are harvested, nutrients which were absorbed by the plants from the soil are also taken away. Continuous cropping and therefore harvesting causes a continuous loss nutrients.

METHODS OF MAINTAINING SOIL FERTILITY

Methods of maintaining soil fertility includes:

(i) Uses of good agronomic practices

- The farmer can improve and maintain the fertility of the soil by adopting good farming methods.

- The aim of using good agronomic practices is to maintain a reasonable level of organic matter in the soil.

- Burning of vegetation leads to loss of organic matter. It is therefore advisable to allow the remains of grass and other plant to die and rot so that they are incorporated into the soil.

In this way organic matter is returned to the soil.

- In nature, the elements nitrogen and carbon circulate through living organism, the soil and the atmosphere. These process are called nitrogen cycles and carbon cycle respectively.

CARBON CYCLE

Carbon is a common constituent of all cell substances and it makes the bulk of the dry matter of all living tissue.

Outline of carbon cycle

(i) Photosynthetic fixation of atmospheric CO₂ by plants and other photoautotroph.

(ii) The release of CO₂ by respiration of plants and animals and microbial decomposition of dead plant and animal residues.

(iii) When the plants and animals die, micro – organism play the essential role in the carbon cycle.

(iv) The dead tissue of plants and animals as well as the excretions from them find their way to either soil or water.

(v) Micro-Organisms of these habitats attack the organic molecule and digest them.

(vi) During microbial digestion, a considerable amount of the tissue carbon is converted to CO₂ and energy is released.

(vii) A part of the energy is used by the decomposing micro-organism for their cell synthesis and the rest is released as heat.

(viii) The CO₂ formed during microbial digestion is the main pathway of its return to the atmosphere to complete cycle.

- Burning of organic materials, as in industry, homes and in bust fires, is another means of returning CO₂.

NITROGEN CYCLE

Nitrogen is an indispensable nutrient for all living cell as it is a constituent of cell proteins.

- This element is always a limiting factor in the growth of plants and animals as it cannot be assimilated by most organism in its elemental form.

- Animals derive their nitrogen from plant source, and plants manufacture their protein mostly from soil nitrogen.

- Most of the soil nitrogen is present in complex organic combination which cannot be used directly by plants.

- One to two percent of nitrogen in the soil is present in organic forms which can be absorbed by plants.

- Ammonium (HH₄⁺) and Nitrate (NO₃) are most inorganic form of nitrogen in the soil.

- Micro-organism plays important role in conversion of organic nitrogenous compounds into inorganic forms. This process is known as MINERALISATION

Def: Mineralization – Is the conversion of an element from an organic combination to inorganic form as a result of microbial decomposition.

- The greatest source of nitrogen is atmospheric nitrogen.

- Part atmospheric nitrogen can be assimilated by certain micro – organism, with or without association of a host. This process is known as BIOLOGICAL NITROGEN

FIXATION

Definition

Biological nitrogen fixation

- Small amout of atmospheric nitrogen may be transformed to ammonium and nitrate for by electric discharges during thunderstoms, the resulting nitrogenous compound being brought down to the soil through precipitation.

- Nitrogen which is fixed biologically reaches the soil in organic combinations.

- Upon the death of the organism affecting nitrogen fixation, their cell nitrogen is acted upon by several micro- organisms and is mineralize.

The mineral nitrogen may be used up by the micro-organism or by plants and be converted to organic nitrogen in the cells. Such process is known as immobilization.

Definition

Immobilization – Is the conversion of an element from the inorganic to organic forms in microbial or plant tissue, thus rendering the element not readly available to other organism or plant.

There is another microbial process that operates under conditions of depleted oxygen supply (anaerobic conditions) where by elemental nitrogen is formed from nitrate and nitrite. This result in volatilization loss nitrogen from the soil, this process is called denitrification.

Definition

Denitrification

- Is the biological reduction of nitrate or nitrite to elemental nitrogen, nitrous or nitric oxide

Nitrification

Definition – Is the biological oxidation of ammonium to nitrate.

- Certain bacteria, known as nitrifying bacteria, use ammonium nitrogen (NH4) as a source of energy and oxidize it to nitrate.

Two groups of bacteria are involved in nitrification

(i) One group oxidize ammonium to nitrate

(ii) The second oxidize nitrate to nitrate

- Bacteria that oxidize ammonium to nitrate include:-

Nitrosococcus

The process is summarized as follows:-

2NH4 + 302 NO₂^- + 4H⁺ + 2H₂0 + energy

- Bacteria that oxidize Nitrite to nitrate include:-

Nitrobacter and Nitrocystis

The process is summarized as follows

2N0₂^- + 0₂ 2N0₃^- + energy

Denitrification

Nitrate is the most oxidized form of nitrogen it can act as an oxidant or electron acceptor.

- In environments where oxygen supply is limited, as under water logged conditions certain micro – organism can use nitrate in the place of oxygen for their respiration.

- In such respiration, nitrate is reduced to elemental nitrogen (N₂), nitric oxide N₂0 and nitrous (N0)

Example:

2N0₃^- + 10H H₂ + 4H₂0 + 20H^-

- There are five agronomic practices which are adopted to maintain the soil organic matter content and therefore, the fertility of the soil at a level which is sufficient for good plant growth. They include

(i) Crop rotation

(ii) Mulching

(iii) Use of cover crop

(iv) Green manuring

(v) Liming

A. Crop rotation

- Is the practice of growing different type of crop on each piece of land each year.

PRINCLIPLES OF CROP ROTATION

a) a crop of a different kind should be grown in each plot each year e.g. Shallow rooted crops should be rotated with deep rooted crops should rotated with deep rooted, legumes with non- legumes.

b) Plants crops which are included in the rotation should be of different families.

c) Valuable crops should if possible follow legumes in the rotation.

d) A fallow period can be included in the rotation.

ADVANTAGE OF CROP ROTATION

(i) When crops with a shallow root system are rotated with deep rooted crops nutrients at different depth in the soil are utilized fully.

(ii) Crop rotation is useful way of controlling weeds e.g. striga grow more easily in field of cerels and when different crops are grown such weed grow with difficulty.

(iii) Crop rotation is a good way controlling plant pest and disease. Plants of the same family are usually attacked by the similar pest and disease. If the crop of a different family is grown the pest and disease may not attack.

(iv) Some plants takes in a lot of nutrients from the soil. Such plants are called heavy feeders. Others take little nutrients from the soil and are called light feeders. By rotating such plants level of nutrients are maintained at a reasonable level.

B. Mulching

- A process of covering soil with a layer of grass, straw and plant remains.

- It is usually used in tree plantation, vegetable gardens etc

Advantage of mulching

1. Mulching helps to conserve moisture by preventing evaporation.

2. Mulching helps to reduce loss of soil erosion.

3. When it rots, the mulching grass or straw adds organic matter to the soil.

4. It helps to control weeds.

Disadvantage of mulching

(i) If the soil I deficiently in nitrogen most of the soil nitrogen is used by the soil micro –organisms which break down the mulching material. In other words plants may compete with micro-organism for soil nitrogen.

(ii) Mulching materials may be attacked by termites or may catch fire, this led destruction of crops as well.

(iii) Extra land may be needed to grow the grass for mulching.

(iv) Heavy work is involved in carrying and spreading the mulch.

C. Cover crops

- Is a crop that is grown in the empty space between rows of plants specifically to cover such as space. In most cases annual or perennial legumes are used for this purpose. E.g. beans.

Qualities of good cover crop

- It should not compete with crop plants for nutrients, water and rooting space or light.

- It should be able to grow well even on poor soil.

- It should drought resistant.

- It should not be an alternative host of insect pest or disease causing organism.

Disadvantages of cover crops

- Protect the soil from evaporation, erosion and therefore improve the infiltration of water into the soil.

- They help to control weeds.

- Most of cover crops are legumes; they help to improve nitrogen content of the soil because bacteria living in the root nodules may fix nitrogen from the atmosphere.

- When they rot, organic matter is added to the soil.

Disadvantage of cover crops

· They may complete with crop plant for water especially during the dry season.

· They may act as alternative host of insect pest and disease causing organism.

· They may compete with crop plant for rooting space.

GEERN MANURING

Green maturing is the practices where by a crops is grown on a piece of land and is then incorporated into soil while it is still green and tender. In most case legumes are used.

B: the addition of materials containing organic matter (organic manures)

Ø Materials containing organic matter are called organic manure or natural manures.

Ø When such substances are added to the soil, the organic matter content of the soil is improved.

Ø Organic manure also adds plant nutrients in the soil.

ORGANIC MANURES

These include

Kraal manure, farm yard manure, poultry manure as well as compost manure.

KRAAL MANURE

This type of manure is obtained form kraals or bomas. These are open enclosures in which cattle are kept especially at night. Kraal consists of fine particles.

When this manure is applied in the soil improves the organic matter content and therefore the fertility of the soil.

FARM YARD MANURE

- It is a good cattle management practice to spread grass on the floor animal shed. Such grass is called bedding.

- The animals deposit their dropping and urine into the grass.

COMPOST

Compost is manure which is made by allowing vegetable matter, plant remains, and grasses etc. to rot in heaps. This has a plenty of hummus.

2.4.2: INORGANIC FERTILIZERS

- Is the substance which contains one or more plant nutrients in a concentrated form.

- These materials are in most cases easily soluble.

- Inorganic fertilizers supply pure nutrients.

- In addition to pure nutrients, they contain other substance which are called filler substance or secondary substance e.g. chlorides, sulphates, trace element etc. these may also favors plant growth.

- Inorganic fertilizers which contain only one of the major elements are called.

Straight fertilizers

- Those which contain all the three major elements (N.P.K) are called complete or mixed fertilizer.

Straight fertilizers

1. Nitrogenous fertilizers

General properties of nitrogenous fertilizers

Ø They may scorch or burn the foliage leaves when they come into contact except urea. Also when they are applied directly on to seedling, they kill it.

Ø Nitrogenous fertilizer encourages vegetative growth.

Ø Most nitrogenous fertilizers are very soluble. Because of their high solubility the residual value of this fertilizer is very low.

Examples of nitrogenous fertilizers

(a) Sulphate ammonia (NH4)₂SO₄

Properties of SA (Sulphate of Ammonia)

§ Consist of small white crystals

§ It contain about 20.5 – 21% nitrogen

§ It is hygroscopic and deliquescent

§ When applied to the soil repeatedly on the field it makes the soil acidic.

(b) Ammonium Sulphate Nitrate (A.S.N)

Properties

§ It is mixture of two salt i.e. ammonium sulphate and ammonium nitrate (NH₄)₂SO₄+NH₄NO₃).

§ It consists of yellowish granules.

§ It contains about 26% sulphur.

§ It does not cause as much acidity as sulphate of ammonia.

Properties

§ It is a mixture of two substance, ammonium nitrate and calcium carbonate

§ It consist of grey granule.

§ It contains about 20% N.

§ It is hydroscopic.

§ It does not cause acidity in the soil.

(d) Urea CO(NH₂)₂

Its properties

§ It consist of white crystals.

§ It contain about 46% N.

§ It very soluble and hygroscopic.

§ It does not scorch plant foliage (leaves).

§ It is easily taken by plant through leaves.

§ It causes very slight acidity in the soil applied repeatedly on the same piece of land.

2. Phosphatic fertilizers

General properties

Ø They are not as soluble and as mobile as nitrogen fertilizers. Foe this reasons they have to be applied close to the roots of plants.

Ø They are absorbed slowly by plant roots.

Ø They do not scorch plant foliage.

Ø They have high residual value than nitrogenous fertilizers.

Ø Encourage development of roots and seeds.

Example of phospahtic fertilizers

(a) Single superphosphate.

Properties

- They are grayish granular substance.

- They contain about 16% - 20% P₂0₅.

(b) Double suprphosphate or triple super phosphate.

Main properties.

- They are grayish granular substance.

- They contain about 43% - 50% P₂0₅

3. Potash fertilizers

Example

(1) Marine of potash (KCl)

(2) Sulphate of potash (K₂S04)

(3) Potassium nitrate (KN0₃).

COMPLETE AND MIXED FERTILIZER

· These contain more than one of the major elements N, P and K.

· Complete fertilizers are manufactured by chemical reactions in a factory. In most cases such fertilizers contain all three elements that is N.P.K.

· Normally complete fertilizers with different proportions of N.P.K are manufacturing for use in different areas according to local conditions.

Examples:

N.P.K fertilizer bag with the number 20:10:10 shown on it means that the fertilizer contain these major elements in the proportions 20%N: 10%P: 10%K.

Ø Mixed fertilizers are prepared by mixing two or even three straight fertilizers mechanically.

Ø Not every fertilizer can be mixed together with another because undesirable chemical reactions occur. For this reason it is important to know which fertilizer can be mixed or not.

Choice of fertilizer to use

- In choosing the fertilizer to use, the following should be considered:-

1) The physical and chemical properties of the soil including the nutrient elements available in the soil.

2) The elements required by the crop grown (or to be grown) at different stage of growth.

3) Type of fertilizer available is including the nutrients which they contain.

4) The price of different fertilizers that is available.

Deciding the quantity of fertilizer to apply

The quantity of fertilizer to apply depends on the following factors.

The chemical and physical properties of the soil including its fertility.

The nutrient content of the fertilizer.

The type crop or crops to be grown.

2.4.3: FERTILIZER CALCULATION

Fertilizer grade: Is determined by knowing how much each of nutrients contained in each fertilizer.

Formula

Percentage of nutrient = Nutrient content X 100%

Total wt of fertilizer

Fertilizer ratio:

It refers to the relative proportioning of nutrients to one another in each fertilizer.

Example:

N:P:K

Will have 1:1:1 ratio of IN, IP (P₂0₅) and IK (K₂0)

Example: 1

Suppose you are required to apply 80kg N/hand the fertilizer available in shop is KN0₃.

Determine the amount of fertilizer to be applied.

Solution:

Percent of nitrogen in fertilizer = A%

Amount of fertilizer to supply 80KgN = (100 X 80Kg)

KN03 = 4 x 100 = 14%

39+14+48

Amount = (100 x 80kg)

= 571kg

Example:2

Suppose you are required to apply 60kgN, 30kg, 30kg P205 and 40kg K20 in a farm of 1 hectare. And the fertilizer available in shop is sulphate of ammonia with 21N, Single super phosphate with 15%P₂0₅ and muriate of potash with 60% K₂0. How much of each fertilizer will you apply in the farm?

Date;

Area of farm = 1ha

Nutrient needed = 60knN

= 30kgP₂0₅

= 40kgK₂0₅

Fertilizer grade:

SA = 21%N

SSP = 15%P₂0₅

KCl = 60%K₂0

Calculations:

Sulphate of ammonia

If 21N = 60kgN

100N = x

100N x 60kg

= 286kg

ii). SSP

15P205 = 30kgP205

100P₂0₅ = x

100 x 30

SSP = 200kg

iii) Muriate of potash.

Kcl = 60k₂0

60k₂0 = 40K₂0

100K₂0 = x

100 x40

= 67kg of Muriate of potash

2:4:4 FERTILIZER APPLICATION

Deciding when to apply fertilizer

- For good results, it is important to supply the nutrients at the proper time.

- The following are general rules that can be followed in deciding when to apply fertilizers.

a) Phosphatic fertilizers are normally applied immediately before sowing or before planting.

This is important because phosphorus is needed for early root formation and development.

b) Nitrogenous fertilizers are normally applied in several small applications two to four weeks after seeds have germinated or after transplanted seedlings have taken roots. This is because nitrogen moves easily in the soil and is required for vegetation growth.

c) Potash fertilizers can be applied before sowing and or 2 – 4 weeks after seeds have germinated.

d) Complete fertilizers especially those with high nitrogen content, can be applied at about the same time as nitrogen fertilizer.

System of fertilizer application

i) Basal dressing – This application of fertilizers at planting time.

ii) Top dressing – This is the application of fertilizers after plant have germinated.

Methods of fertilizer application

1. Broadcasting

This is the uniform distribution of fertilizer over the soil.

When should this method be used?

i) On close growing crops which are not grown in rows.

ii) On very fertile soil.

iii) When easily soluble nitrogenous fertilizers are applied.

iv) When large quantity of fertilizers are applied.

v) On plants which produce extensive root system.

2. Band application

This is done by applying fertilizer in strips (band) along the rows of plant.

3. Placement

This is done by applying fertilizer in pockets in the soil close to plant roots.

When should placement and band application be used?

i) On plants with wide spacing.

ii) On soil with low fertility.

iii) When applying less readly soluble fertilizers.

iv) When applying potash and/or phosphatic fertilizers on soils in which there are possibilities of potash and/or phosphate fixation to take place.

v) On plants which produce only a few roots.

vi) When applying small quantities of fertilizer.

4. Foliar fertilization

Plant nutrition

Sixteen elements are essential for normal plant growth.

- Some elements are required in large quantities and are called MACRO –NUTRIENTS

- Some elements are required in small quantities and are called micro – NUTRIENTS or

TRACE – ELEMENT.

Macro – elements

· Carbon

· Oxygen

· Hydrogen

· Nitrogen

· Phosphorus

· Potassium

· Magnesium

· Calcium

· Sulphur

Micro – elements

· Manganese

· Iron

· Boron

· Molybdenum

· Copper

· Zinc

· Chlorine

Function of the nutrients in plants

Carbon

§ Tissue of all living organism contain carbon.

§ Plants take in carbon in the form of carbon dioxide from the atmosphere through stomata.

§ In presence of sunlight and water, the green parts of the plant convert the C0₂ into carbohydrates.

Hydrogen and oxygen

- Plants taken in oxygen and hydrogen in the form of water.

- Water id necessary for the life of plants.

Nitrogen

- The quantities of nitrogen taken up by plants are large than those of any other nutrients.

- With the exception of plants which can fix atmospheric nitrogen because of their association with nitrogen fixers, most other plants take up their nitrogen in a form other than elemental (free) nitrogen.

- The forms absorbed are mainly the ammonium (NH₄⁺) and the nitrate NO₃^-ions, although small quantities of urea, water soluble amino acids amides have been shown to be absorbed by plants.

Functions

Ø Nitrogen is an important constituent of protein which present in protoplasm of plant cells. E.g. enzymes.

Ø Nitrogen is important constituent of chlorophyll.

Ø Nitrogen application has been shown to increase uptake of phosphorus, potassium and calcium.

Ø Stimulate vegetative growth and encourages the development of good quality leaves.

Effect of excessive application of nitrogen

(i) It may delay maturity by encouraging excessive vegetative growth.

(ii) It may lower the yield of grains and fruits.

(iii) It may weaken the straw and encourage lodging in cereal crops

(iv) It may make the plants more succulent and therefore less resistant to disease and pest attack.

Deficiency symptoms of nitrogen

Ø Stunted growth and yellow in appearance. (chlorosis)

Ø If the deficiency continues, the leaves turn brown and finally die.

Phosphorus

Plants take up phosphorus in smaller quantities than either nitrogen or potassium.

Functions

(i) It promote the formation of roots and seeds, it stimulate flowering.

(ii) It promotes the formation of tillers in crops such as sorghum, millet and paddy and therefore, increase the grain yield of such crops.

(iii) It makes straw stronger and therefore more resistant to lodging

(iv) It improves disease resitance in plants.

(v) It is essential for Rhizobium bacteria living in roots nodules of legumes which fix nitrogen from the air.

Potassium

- The quantities of potassium found in most plant tissue are close to those of nitrogen, thus making potassium the second elements needed by plants in large quantities.

Function

(i) It is essential in formation of carbohydrate and the translocation of starch to various parts of the plant.

(ii) It encourages normal cell division in young plant tissue.

(iii) It strengthen the straw and stalk of cereal plants in this way.

(a) Increase the resistance of plants to disease causing organism such as Fung and Bacteria.

(b) It makes the plants more resistant to lodging.

(iv) It plays an important role in water regulation in plants.

Potassium deficiency symptoms

Ø Leaves become dry and scorched at the edges while the rest of the leaf surface becomes chlorotic.

Calcium

Functions

Ø Calcium is the constituents of cell wall of plant. A substance called calcium spectate helps in the formation of middle lamella. In this way it strengthens the cell walls so that the straw become stiff and resistant to lodging.

Ø Calcium neutralizes organic acids such as oxalic acid in plants.

Ø Calcium promotes seed production.

Ø It regulates the uptake of potassium by plants.

Ø Its is essential for normal cell division.

Calcium deficiency symptoms

Ø Terminal bunds of shoots and apical tips of roots fail to develop and therefore growth of the plants stops.

Ø Plants shed buds and flowers prematurely.

Magnesium

Functions

Ø It is part and parcel of the chlorophyll molecule.

Ø It regulates the uptake of nutrients, for example, it promotes the uptake and translocation of phosphorus.

Ø It helps in translocation of carbohydrates in the form of sugars in plants.

Ø It is involved in phosphorus metabolism in plants.

Magnesium deficiency symptoms

Ø The veins of old leave remain green while the area between the veins becomes chlorotic.

Ø If this continues, the leaves become uniformly pale yellow and then turn brown and die.

Sulphur

Functions

- Sulphur is an important constituent of certain vitamin in plants e.g. vitamin A.

- It is required for formation of amino acids which contain sulphur e.g. cystine, cystein and methione.

- It activates protein – digesting enzymes e.g. papainases.

Deficiency symptoms of sulphur

Ø Plant growth is returned.

Ø Plants become thin stemmed, rigid, brittle and stunted.

Ø Younger leaves become yellowish green or chlorotic.

Manganese

Function

Ø Manganese is necessary for the formation of chlorophyll.

Ø It acts as catalyst in many metabolic reactions such as reduction of nitrates, respiration and synthesis of chlorophyll etc.

Deficiency symptoms of manganese

Ø Leaf vein remain green while areas between the veins become chlorotic.

Iron

Function

· Essential in the formation of chlorophyll.

· It is a constituent of various enzymes.

Deficiency symptoms of Iron

· Young leaves of plants first become chlorotic in areas between veins.

· Later on the leaves turn completely white.

· It is an essential catalyst in the productions of chlorophyll.

Molybdenum

Function

· Molybdenum is required by Rhizobia for nitrogen fixation in legumes.

Deficiency

· Areas of leaves between vein become chlorotic.

· Legumes normally turn yellow and become stunted.

Boron

· Boron is required for the formation of flowers, fruits and roots.

· It is also necessary for the translocation of substance within the plant.

· It is essential for protein synthesis.

Deficiency symptoms of boron

· The younger leaves become pale green in colour especially at the bases.

· Growing points of plants become deformed and stop growing.

Copper

- Copper is involved as an activator or electron carrier in respiration.

- It is also important in the utilization of iron by plants.

- It promotes the formation of vitamin A in plants.

Deficiency symptoms

Leaves turn yellow and plants become stunted.

Zinc

Function

- Zinc acts as an activator and help in the formation of growth hormone.

- It plays a role in acidic soil and protein synthesis.

- It acids the utilization of nitrogen and phosphorus in plants.

Symptoms of deficiency

- Young leaves shown interveinachlorosis followed by reduction in the rate of growth of shoot which leads to rosetting.

2.5 : WATER SUPPLY, IRRIGATION AND DRAINAGE

Ø Introduction

Water plays a fundamental role in agriculture. It is essential for livestock and it forms large par of all plants tissue. Very large amounts are transpired by plant these carry nutrients from the soil to the plant tissue in process. Water can be useful in other ways, such as the transport of produce, the generation of electric power, the operation of water wheels for grinding grain, the removal of heat in cooling and the cleaning of produce such coffee. Although water has many beneficial used it can also cause very great problems.

It causes water logging which retards plant growth. It is the main agent of soil erosion in East Africa and the flooding of rivers causes periodic damage to crops and endangers the lives of people. The demand for water is increasing for domestic use, for irrigation and for industrial process.

Ø Animal water requirements

Water is the essential component of all body cells and activities. Thus all animals should have ready access to water at all times. Death from water shortage ensues after a few days or weeks, while death from food shortage only occurs after a long period of time. Water is the most limiting factor for grazing animals in many farms. Ideally there should be a water point no further than 0.8km from very grazing area. Shortage of water also affects the quality of the grass and fodder consumed by any grazing animals, and during times of drought, expensive supplements many have to be fed.

Animals raised indoors must water through adequately filled at all times.

In practice it is not always possible to supply sufficient water, since many areas are very dry. Permanent watering facilities are required.

Ø Crop water requirements

When planning irrigation, it is important to be able to estimate the daily consumption of water by the plant and the frequency with which irrigation should be applied. The consumption of water by the plant depends on several factors, such as the level of moisture in the soil and the stage of growth of the plant. However if a green crop completely covers the ground and is growing actively in soil which is freely supplied with moisture, the use of water is dependent almost entirely on meteorological factors, of which hours of sunshine, wind speed, temperature and relative humidity are the most important. Although most of the water is lost through the leaves of plants by transpiration a certain amount is also lost by evaporation from the leaf surface and from the ground and the term evapotranspiration is used to cover the combined loss of water from the crop and the ground.

Estimation of evapotranspiration can be made from meteorogical data, or by measuring the actual loss of moisture by transpiration from an open surface of water because the numerous tiny holes (stomata) in the leaf surface offer little resistance to the movement of water vapour from the water-filled tissue underneath. Any estimate of evapotranspiration must take account of differences between crops, which arise from variations due to stage of growth, spacing, height, leaf characteristics and availability of moisture in the soil.

The frequency with which water must be applied will depend on the rooting depth of the crop and the water holding capital of the soil. Shallow rooted crops such as cabbages or beans will need more crops frequent applications of water than deeper rooted crops such as coffee or cotton. Crops grown in sandy soils which hold little water will need more frequent applications than crops grown in clay soil which hold much more water.

Only a small part of East African has an adequate supply of water and the development of agriculture and industry depends to a great extent on the development of the water resources. The way in which water circulates from the earth to the atmosphere and back to earth is known as the hydrological (water) cycle and an understanding of this cycle is important in any study of water supply.

Ø The water cycle

The hydrological cycle is depending in fig. 19.1. The energy of the sun is responsible for the movement of water from the surface of the earth into the atmosphere as water vapors where it cools, condenses and forms clouds. It returns to the earth as precipitation (rain, hail, snow). On reaching the earth it may be intercepted by plants before reaching the ground and return by evaporation to the atmosphere. It may enter the ground (infiltration). Having entered the ground, water may be held in the soil as soil moisture and either evaporate slowly from the surface of the soil or be taken up by plants (transpiratiuon). The combined loss by plants and directly by evaporation is known as evapotranspration . If more water enters the ground than the soil can hold if it many move laterally through the soil (through flow) especially if there is an impermeable layer preventing deep percolation. Through flow may emerge as springs at a place which is lower and some distance from that at which infiltration occurred or it may seep out into stream channel. Water which percolates deep into the earth’s surface is known as ground water. It may be utilized by pumping out from deep boreholes. Wherever water saturates the soil so that air is removed, it forms an acquifer and the top surface of this water- bearing zone is called water table. Sometimes this water table is perched on an impermeable layer. During heavy rain it may be near the surface and at other times it may be several hundred metres below ground.

Ø Rainfall

The farmer is interested in the amount and distribution of rainfall and in the intensity of rainfall. Rainfall amount can be measured by rain gauges of which the simple kinds are used for daily measurements (see fig 19.2) and the more complicated kinds record rainfall on a rotating graph. Train gauges record the rain which falls on a very small part of the earth’s surface and several gauges are needed to give an accurate representation of rain falling in a given area. It is also very important to place rain gauges in a level position and at a distance from any object such as a tree or building which is at least twice the height of the object. Reading should be done at the same time, usually 9.00 a.m. each day. Rain collected in the gauge is poured into a calibrated measuring cylinder. As the diameter of gauges varies, it is important to use the correct measuring cylinder.

Rainfall intensity is the amount ram falling in a certain period of time and is expressed in mille meters per hour. High rain, of 100 mm/hr usually only occurs for short period of 10-15 minutes. In general the storm the lower the average intensity. farmer is concerned about rainfall at intensities than 25 mm/hr, because such rainfall is to cause soil erosion. Approximately 85% of Kenya’s land surface re- rainfall which is either insufficient for crop or is adequate in some years but not in.In such areas the farmer should adopt park- which reduce surface runoff and increase

Ø Surface runoff and inﬁltration

The proportion of rain which is lost through surface run off depends on the vegetative cover of the ground, the condition of the soil surface, the per-me ability of the soil and the slope of the ground. When soil is exposed to heavy rainfall the surface is beaten down and ﬁne particles of soil block the pores through which water would otherwise inﬁl- trite. When the soil dries out the surface appears smooth and hard and is said to be ‘capped’. The run off rate from bare capped soil can be very high and at least 50% of the rain which falls during as term may be lost as a result. Under a close vegetative cover of trees or crops, runoff is reduced.It is often thought that trees increase rainfall, but there is no sciatic evidence to support this theory. What does happen however is that when trees are cut down inﬁltration is reduced and surface runoff increased. As a result streams which once ﬂowed all year round may cease to ﬂowed in the dry season. Inﬁltration can be promoted by incorporating organic matter such as plant residues in the soil and by leaving the surface of the ground rough. Surface runoff can be reduced by sloughing and planting on the contour. Terracing which alters the slope or the length of slope of the land can also assist in reducing runoff and increasing inﬁltration.

Ø Evaporation and Evapotranspiration

Water can evaporate very quickly from the surface of wet soil but once the top centimetre is dry, the rate of loss is very much slower and almost stops when there are 10— 15 cm of dry soil on the surface. However, plants act like pipes through which soil moisture is drained out of the ground and if there is a close cover of plants and the ground is wet, water will be lost nearly as fast as it would be from an open surface of water, such as a lake. Evapotranspiration may amount to as much as 5 mm per day, or more in dry weather. A rain storm, or irrigation which provides a crop with 50mm of rain could therefore be used up in as little as 10 days.

2.5.2: WATER SUPPLY

NB: water is very important natural resource

Ø It necessary for both crops and livestocks that can be used as

a) Cleaning equipment

b) Irrigation in dry area

c) Processing farm produce ,for example coffee

d) Drinking by livestocks and man

e) Mixing of Agro-chemicals such as fungicides and pesticides

f) Providing power in water mills to grind grains crops

g) Cooling engine

h) Construction purposes

Sources of water in farm

a) Surface water :this include water from rivers,strems and dams

b) Rain water :this is water that can tapped by roots tops and rocks surfaces ,when it is raining and stored in various way

c) Graund water ;this include water from springs ,wells and boreholes .

Collection and storage of water

Ø Dams ;these are structures constracted across rivers and channels .they collect and store water for use during the dry season

Ø Weirs ;these are structures that constracted across rivers to raise the H2O level for easy pumping Unlike in the dams water flows over the barrier created across the river .

Ø Water tanks ;are structures made of concrete,stone,metal sheets and plastics. They store water from rain or that which has been pumped from other sources. It should covered to avoid contermination

Ø Wells ;these are structures like dams but they are small and they may collect water from rivers

PUMPS AND PUMPING OF WATER

Pumping ;is the lifting of water from one point to another by use of mechanical force .water is pumped from the various sources and then converged to where it’s required for use or storage

Types of pumps (water pumps)

Ø Centrifugal pumps

Ø Piston or reciprocating pumps

Ø Semi rotary pumps

Ø Hydrae

Conveyance of water

This is the process of moving water from one point ,usually the source or point of storage to where it will be used or stored

Ø There are different ways of conveying water as follows

a) Piping ;this is where water is moving through pipes .there are different forms of pipes such as-metal pipes

-plastics pipes

-hose pipes

b) Use of containers ;this is where as water is carried by using containers such as chums ,jerry can ,pots ,buckets and tanks that can be carried by human ,donkey ,bicycle or vehicle

c) Use of channels ;this is conveying of water from high area to place of low land area through slope .mostly use of this method use for irrigation and live stocks

d) Use of airplane ;these is conveying of water where as an airplane can tape a water from source and transform it to farm .also this method used for large irrigation

e) Rain cycle ;this is where water evaporates from seas and then after several process is retuned as rain full.

Ø Ground water

If the rainfall which inﬁltrates exceeds the storage capacity of the soil it will move downwards until it reaches a zone of saturation which overlies an impermeable layer. The surface of this saturated zone is known as the water table. It may be near the surface or many hundreds of metres below. A perched water table is sometimes found where there is more than one impermeable layer. Lake Naivasha is an example of a perched water table which over-lies an unsaturated zone below which is the main source of ground water. The ground zone which is saturated and from which water can be obtained from wells or boreholes is known as an aquifer. Where there are two impel- me able layers which are sloping, water may become trapped between them in a conﬁned aquifer. Such water may be under considerable pressure and if the upper layer is penetrated by a borehole Water will rise up and may, if the pressure is great enough, reach the surface without pumping.

Ø Water sources and supply

Water may be obtained from surface Water sources such as rivers, streams, lakes, reservoirs, or from ground water sources such as springs, shallow wells or deep boreholes. It may also be obtained by collecting rain water directly from roofs.

Ø Surface water sources

Obtaining a supply of water from a river or stream often requires the construction of a weir or a dam. The difference between a weir and a dam is that the former is designed to raise the water level in the stream, but to allow water to continue ﬂowing over the top. A dam is designed to impede the ﬂowing of water and store as much as possible. Flood water is allowed to pass the dam through a specially designed spillway, but not normally over the top of the dam wall. Weirs may be constructed from loose rocks sometimes held together by wire mesh, or from logs (ﬁg19/3(a). Such weirs are semi-permanent, but cheap to construct. Permanent weirs can be made from concrete. They should, if possible, be constructed on rock foundations and must have a rock or concrete surface onto which water can fall, otherwise scouring will occur on the lower side andthe weir will be undermined. Dams are normally bigger structures than weirs and must be able to withstand much greater forces. The embankments are usually made of earth, but in order to prevent seepage, the centre core of an impervious material such as soil with a clay content A good grass cover is required earth dams and stones may be needed on the side to prevent wave action eroding the emend Trees and bushes must not be allowed or Embankment, because the roots can lead to and eventually breakage Some dams such as Kamburu dam on the Tana river are made rocks and seepage 1S prevented by lining the upper side with concrete slabs and asphalt.

A sub surface dam is a special kind of dam made of concrete which is constructed on a rock foundation across the bed of a sand river It is used in dry areas to store water m rivers which only flow for part of the year Sand collects behind the dam wall and Water is stored m the sand Although the volume of water which can be stored is obviously less than in an ordinary dam, evaporation is low and ﬂood waters can pass over the top of the wall without causing damage A farmer may improve the water supply of a farm by damming a small stream and piping the excess water to a trough for storage. Loose rocks and stones may be used for the purpose, so expense in minimal. example a dam at china as seen bellow

Ø Ground water sources

Springs

Springs may arise where an impermeable layer meets the ground surface Springs are particularly valuable, as the Water is usually uncontaminated and if the spring is on a hillside, water may is usually uncontaminated and if the spring is on a hillside, water may be gravitated to dwellings lower down. Development of a spring usually involves constructing a low wall around it to increase the depth of water. Protection from livestock is extremely important and water should be drawn out through a pipe rather than directly from the spring itself to avoid contamination

Wells

wells are usually dug by hand and not more than 15 m deep though some very deep wells are found in the North Eastern Province. Wells should be dug in the dry season when the water table is low. If a lining is required it may be constructed from brick or stone and may be built from the bottom up if the ground is stable or from the top downwards using a concrete ring or curb as base. A common method is to use concrete culverts which are lowered by undercutting as the well is dug. A broad concrete slab is desirable to cover the well and

Adjacent to it to prevent contamination.

Boreholes

Boreholes can be drilled by hand if they are shallow, but power driven machinery is required for deep boreholes. The hole is normally lined with a casing which is perforated at the lower end to allow water to pass through. Ordinary pumps cannot lift water more than about 6m at sea level and less at higher altitudes. It is therefore necessary to put the pump down in the borehole and as the water table ﬂuctuates the pump should be below the surface of the water. Submersible pumps are electrically driven pumps which are designed so that the pump and motor can be placed below the water level.

š Collection of rainwater

In areas where water is scarce the collection of rain water can be important and valuable amounts can be collected from roofs. Special catchments are sometimes made from asphalt or plastic to collect rain water. The farmer can improve his water supplies by catching rain water from the roof and storing it in barrels. In order to calculate the volume of storage required, it is necessary to know the horizontal area equivalent to the roof or catchment and to multiply by the depth of rain expected. However if a seasonal rainfall ﬁgure is used, allowance must be made for

the fact that some water will be used during the rainy season. Water can be stored in earth reservoirs which may be lined with polyethylene or butyl rubber to reduce seepage. Stone tanks are commonly used, but must be reinforced to withstand pressures. The tank ﬂoor is usually reinforced with weld mesh and several strands of high tensile steel wire are put

Between each course of stone.

Ø Water lifting

Water lifting devices are of many kinds but they can be classier as follows:

· Rot dynamic pumps e.g. centrifugal pumps;

· Reciprocating pumps e.g. piston pumps;

· Rotary or semi-rotary pumps and

· Other lifting devices e. g. hydram.

Centrifugal pumps have an impeller, a metal disc with blades (vanes), which rotates at speeds of

1 500-3 000 revolutions per minute. Water is driven by centrifugal force to the outlet. Such

pumps are particularly suited to irrigation because they can pump large quantities of water. In multi- stage pumps, several impellers are used on the same shaft to give high pressures. Piston pumps have no evolved and can be used to pump dirty water, which would quickly wear out a piston pump.

If a pump is new or has been out of action for sometime it will be necessary to prime it before it

can work. This means ﬁlling the suction pipe with water. At the lower end of the suction pipe there should be a foot valve which prevents water from leaking out of the suction pipe when the pump is stopped for a short period. Semi-rotary pumps are often used for pumping water by hand from shallow wells.

A hydram is a special kind of pump which is driven by the action of falling water. Water from a

stream is channeled into a drive pipe through which it falls at considerable speed. At ﬁrst water

passes through the escape valve but as its speed increases the escape valve shuts abruptly and the

sudden increase in pressure forces water‘ through a second valve into the delivery pipe. Hydrams can pump relatively small quantities of water to considerable heights and at negligible cost. They are suited to places such as steep valleys, where sufficient height can be obtained for the required fall of water. Obviously a proportion of water which goes into the ram passes into the delivery pipe. The remainder returns to the stream or river.

Ø Water conveyance

Water can be conveyed in pipes or channels. Pipes have the advantage that they can carry water under pressure and can go uphill or downhill. Channels must be on an even gradient (slope), but can be useful for carrying large quantities of water. The Romans used covered channels made of stone called aqueducts to supply towns. Whether water is following in a pipe or channel the following equation expresses the follow:

=VA

= rate of ﬂow in m3/s

where

I><,0,0

velocity of ﬂow in m/s

= cross sectional area in m2

Various kinds of pipe are available. Galvanised iron pipes were used very widely, but due to high

cost are now only used where high pressures or exposure to sunlight would make plastic pipes

unsuitable. Plastic pipes are made from P.V.C. (polyvinyl chloride) or P.E. (polyethylene). They are much smoother than iron pipes, are easily joined, and cause much less friction loss.

They resist corrosion, but P.V.C. piping can be dam-aged by sunlight. P.E. piping can be damaged by

rodents. When purchasing it is necessary to know the pressures which the piping will have a withstand and to obtain a suitable thickness.

Ø Water treatment

Water may be unsuitable for domestic use for a variety of reasons. It may have chemical

impurities such as ﬂuorine or chlorine which are harmful in excess, or it may have a high bacteriological content Bacterial diseases such as typhoid and cholera can be spread by dirty water. In addition water may be unsuitable on account of sediment or an unpleasant taste or odour.

in general ground water supplies are free from bacteria and sediment but sometimes have chemical

impurities. Surface water supplies are more likely to have a high bacterial content and sediment, but usually have a lower content of chemical impurities.

The simplest water treatment consists of storing water for a period which will allow sediment

to settle and will also reduce the bacteriological content. The bilharzia organism cannot survive in

water which is stored for more than 36 hours. If water is ﬁltered slowly through a sand ﬁltered exposed to light, the sediment will be deposited and bacteria

are removed in biological processes which take place on the surface of the sand. Water from such

ﬁltered is normally safe to drink.

To guarantee the safety of water for domestic use it is customary to add very small quantities

of chlorine in the form of bleaching powder, chlorinated lime or sodium hypochlorite. Water for livestock need not be treated, but should be protected from pollution and piped to a trough.

Ø Sanitation

The use of water for sanitation can play a very big part in preventing the spread of diseases.

However the type of waterborne sanitation found in town and cities requires relatively large amounts of water and is expensive to install.

With waterborne sanitation, each house must have a septic tank or be connected to the municipal sewage system. A septic tank is simply an underground tank lined with concrete blocks or stone into which all domestic waste can ﬂow. Biological decomposition of organic matter takes place in

the tank and the surplus water (effluent) which passes out into a drain is free from harmful or unpleasant effects.

In rural areas which are short of water the aqua prim; can be used.

This is similar to a septic tank with a toilet constructed directly over it. Only small quantities of water are required. An alternative method is a pit latrine with a water seal closet.

This requires very small amounts of water for ﬂushing and prevents the breeding of ﬂies and mosquitoes.

WATER TREATMENT

Raw water can contain impurities at different states as follows

v Physical impurities :this are touchable ,testable ,smell able and a color in the water

v Chemical impurities :are dissolved impurities detected by chemical means

v Biological impurities :this include microorganism such as bacteria ,viruses and algae

METHODS OF TREATING WATER

Ø Aeration :This is smell and dour from water by fine spraying and bubbling of air

Ø Sedimentation :is the separation of large particles from water by allowing water to settle until sediment remain down the container

Ø Filtration :is the separation of contaminant from water by using filter paper within it

Ø Coagulation :is the addition of chemicals which precipitate impurities and help in softening of hard water

Ø Chlorination :is the destruction of diseases and microorganisms from the water by using specific purifier

2.5.2 :IRRIGATION

Introduction ;Is the artificial application of water to the crops from where it’s an adequate water supply

NB ;factors for irrigation

Ø Topography of an area

Ø Availability of water

Ø Types of soil

Ø Types of crops grown

Ø Human factor (skill capability )

Ø Availability of equipment

TYPES OF IRRIGATION

1. SURFACE OF IRRIGATION

This is application of water by gravity slope flow to the surface of the field

(a)Furrow irrigation

(b)Basin irrigation

(c)Border irrigation

(d)Wild flood irrigation /free flooding

a) Furrow irrigation ;It conducting by small channels

ð Crops that irrigated by this method

Ø Row crops such as maize, sugarcane, and soya beans

Ø Broadcast crops such as wheat

Ø Demaged crops such as tomatoes, vegetables, and potatoes

ð Advantages of furrow irrigation

Ø It’s easy and cheap

Ø Adaptive in wide land slopes expect flat land

Ø It supply a lot of water

Ø It may perform large area for short period

ð Limitation of furrow irrigation

Ø It only applicable in row crops

Ø It’s not applicable in flat land

Ø It cause soil salitation

Ø It consume higher amount of water compare to sprinkler

5(a)Briefly describe furrow irrigation system

(b)outline three advantages and four disadvantages of furrow

(c)suggest four necessary condition for surface irrigation

Qn. necta 2018

b) Basin irrigation; Is the application of water on flat low land .that water suspended on land .

Ø The crops which are irrigated are ;paddy, cloves, citrus tree, and pasture such as alfalfa

ð NB; Basin size should be small if

Ø Slope of land is steep

Ø Soil is sandy

Ø Stream size to basin is small

Ø Required depth of irrigation application is small

Ø Field preparation is done by hand or animal technique

ð Basin size should be large if

Ø Slope at land is flat

Ø Soil is clay

Ø Stream size to basin is large

Ø Required depth of irrigation application is large

Ø Field preparation is mechanical

ð Advantages of basin irrigation

Ø It conserve rain water

Ø It reduce soil erosion

Ø High application of water and efficiency is distribution

Ø It may cause leaching of salts (applicable in salt leaching )

ð Disadvantages of basin irrigation

Ø It require high labor provision

Ø It’s not applicable for damaged crops

Ø It may cause fungal disease to labor or same crops

Ø It may led leaching of nutrients instead of that salt to be leach only

NB; filling of basin with water done by single plot method ,that water enters the individual basin .and plot to plot mathod ,that water fill in the frequency of plots from plot to plot

(c)Wild/Free flooding irrigation ;is the method that water are derivared from the source and that allowed to flow over the crops field (unplanted field)

ð Advantages of flooding

Ø Labour required is minimum

Ø The system is very easy than others

Ø It may destroy weeds

Ø It supply a lot of water

ð Disadvantages of flooding

Ø It consume water

Ø It’s uncontrollable

Ø It’s not efficiency (some areas get water others lack)

Ø Result on soil erosion

Ø It cause high infiltration

(d)Border irrigation ;this is the flooding that controlled by border .it’s the application of water that water moves slowly at channels and diverted in to strips as moving

NB;this method used in planted crops ,similar surface soil and slope that water may flow.

ð Advantages of border irrigation

Ø It’s easy to control

Ø Labour required is reduced compare to basin

Ø It apply large amount of water

Ø Crops and lobours disease is reduced

Ø It’s simple and easy

ð Disadvantages

Ø It’s not suitable for sand soil

Ø It may lead soil erosion

Ø It consume water

Ø It may cause infiltration

2. SUB-SURFACE IRRIGATION

This is the application of water bellow the ground so that water can supplied directly to root zone of the plants

Ä It’s divided in to natural irrigation and artificial irrigation

NB; Natural sub-surface irrigation includes

Ø Underground water (swamps area)

Ø Spring

Mechanism ;there are same soil in a particular areas (swamps areas)contain water naturally so the areas like that does not used more application of water

Advantages

Ø Farmers may calculate allover the year

Ø Different crops are applicable

Ø Water application is efficiency

Ø There is no soil erosion

Disadvantages

Ø It may increase weeds (if not controlled )

Ø It may cause water logging for some crops

Ø Some area contain salt underground water (cause distruction of crops )

NB; Artificial sub-surface irrigation includes

Ø Drip (trickler irrigation )

Mechanism ;water allowed at low rate from emmiters and drippers to a plant roots.only roots area get wet and methods is very efficiency

v Drip irrigation loyout

¯ Pumps unit ;take water from the source and direct on pipe

¯ Control head

¯ Main and sub main lines ;direct water to laterals

¯ Laterals ;small lines direct water to drippers

¯ Emmiters and drippers

Are small diameter openings in the laterals which provide water to plants

Ø The numbers of emmiters per plant depends on the size of plant

Y Small plant example ;vegetables used only one emmiter per plant

Y Tree crops requires several emitters per plant

Advantages of artificial sub-surface irrigation

Ø It’s conserve water (does not use a lot of water)

Ø The efficiency in application is high

Ø It minimize soil erosion

Ø Elimination of many diseases

Ø Field leveling is not necessary

Disadvantages of artificial sub-surface irrigation

Ø High cost to establish

Ø There is the danger of water logging

Ø Possibility of pipe cracking or rusting underground

3. OVERHEAD IRRIGATION

The water is applied from above the soil surface in drops or splash. It similar to natural rainfall

ð It is more applicable in the following areas

Ø There are scarcity of water

Ø Where as uniform water application is required

Ø Sand and shallow soil

Ø It can used in variable topography

Y NB; It suits almost the soils but: application rate should be less than infiltration rate

Y NB; It suits almost all the crops but

The drop size should proportional to crop type example delicate crops such lettuce used small drops

Ø The overhead irrigation have two case studies which is

Ø Sprinkler irrigation

Ø Air plane irrigation

(a) SPRINKLER IRRIGATION

Sprinkler irrigation

Where land is too steep, topography uneven or soils very permeable, sprinkler irrigation is more suit-able. The cost of overhead irrigation will often greater on account of the need for pumping and the capital expenditure on equipment, but if the scheme has been well designed, the distribution of water may be better than with surface irrigation and less water is wasted through seepage from canals and ditches. In certain hilly areas it is possible to supply sprinklers by gravity, but a constant pressure is necessary if sprinklers are to operate efﬁciently. Sprinkler irrigation is liable to encourage disease in certain crops e.g. tomatoes and increase the need for control by fungicides and if winds are high the distribution of water from sprinklers is liable to beuneven. Shelter belts of trees will reduce the latter problem.

Where water is in short supply, drip irrigation has many advantages. Water is supplied through polyethylene pipes to each row of plants and a small nozzle allows water to drip out and maintain a moist zone around the plant roots. By this method the plant root zone is never dry and never water- logged and plants are protected from the damaging effect of high salt concentrations which are found in some soils. As water is not spread over the whole surface, weeds are not encouraged between plant rows and losses from evaporation and seepage are reduced to a minimum.

Difinition

sprinkler irrigation:the water is applied to the crops in forms of drops or natural rainfall through sprinklers .this may done by the following loyout

Sprinkler loyout

Ä Pumps units: takes water from the source and direct to the pipelines

Ä Main lines: dilivers water from pumps unit to the laterals

Ä Laterals :it dilivers water from pipeline to splinklers

Ä Sprinklers :it deliver water from laterals to the plant by spraying in form of rainfall or drops

ð Advantages of sprinkler irrigation

Ä It does not require land leveling

Ä It can used in areas of different topography

Ä Chemicals and fertilizer application are easy by using sprinkler system

Ä High efficiency of water application

Ä It conserve water (small amount of water used )

Ä It minimize soil erosion

ð Disadvantages of sprinkler irrigation

Ä It require very clean water

Ä It affected by wind and high temperature

Ä It needs high initial cost

Ä It require skilled person

Ä Energy is required for operating system

NB; The drop size is controlled by operating pressure and nozzle size

Small nozzle diameter –small drop size

Large nozzle diameter –large drop size

Usually water breaks up to small drops between 0.5 and 4.0 mm in size diameter .small size drops fall near the sprinkler but larger moves away from the sprinkler

(b)Air plane irrigation : this is the use of airplane on applying water to crops on the same water rate required by crops .water drops in form of natural rainfall

This is more advantages method used by developed countries

Advantages of airplane irrigation

Ä It supply water efficiently

Ä It’s very fast and perform a lot of area

Ä Chemicals and fertilizers are easy to apply

Ä It can used in area of different topography

Ä It require one skilled labor

Disadvantages of airplane irrigation

Ä It has high initial cost

Ä It require clean water

Ä It used skilled person to operate airplane

Ä It has progressive cost for fuel to operate engine

Application of irrigation

The amount of water which can be held in a soil and used by plants (available water) can be ex-pressed as a percentage by volume or as a depth per metre. When soil is fully wetted (but allowed to drain and therefore not saturated) it is said to be at ﬁeld capacity. When it is so dry that plants wilt permanently, it is said to be at Permanent Wilting Point. If or example a soil has 25% moisture (by volume) at held capacity and 15% moisture at wilting point, the available moisture in the root zone would be 10% i.e. 100 mm per metre depth. Ifa crop roots to 1 metre depth and evapotranspiration takes place at Sun per day, the available water would be used up in 20 days (assuming there wereno rain). In normal practice it would be unwise to allow a crop to reach wilting point before irrigating because growth would slow down. Irrigation should therefore take place when not more than half the available water has been used. In the above example therefore it would take place every ten days and at each irrigation the crop would be supplied with not less than 50mm of water. As some water may be lost due to evaporation and some may percolate below the root zone it is necessary to apply from 10—Z0% more water, i.e. 55-60mm, to make certain that the plants receive sufficient. In practicemany farmers do not know how much water they are applying and either put on too much or toolittle, both of which can cause serious problems.

When waste: is applied in furrows there is always a danger that too much water will soak in at the upper end. Water only moves slowly down the furrow because the upper end will be wetted for a longer time. It is recommended that furrows should be laid out with sufficient slope so that water can reach the lower end in one quarter of the total wetting time. However too much slope could lead to erosion. A further problem may arise if too much water accumulates at the lower end of a furrow and causes water logging. This can be avoided by using 2 or more siphons to wet the whole furrow quickly and then reducing to one siphon for the main period of irrigation.

When water is applied from sprinklers it should be supplied at the correct pressure and thesprinklers should be spaced according to the manufacturer’s recommendations, which normally allows a50%~60% overlap. Periods of high wind which cause uneven distribution should be avoided and if sprinkling can be carried out at night, losses from evaporation will be reduced. When capital is short it is normal to use a limited number of portable pipes and sprinklers which can be moved from one ‘set’ to the next. Sprinkler application rates are usually about 12.5 min per hour so that 4—5 hours per set may be required to put on sufficient water .In parts of the world where labor is expensive or high income crops are grown, farmers ﬁnd it more economical to install permanent pipes and sprinklers. Although drip irrigation has many

Advantage the capital costs involved are even greater than for sprinkler irrigation and preclude its use for any but the most proﬁtable crops.

As mentioned earlier irrigation schemes are not ways successful and the main problems arise due-to the incorrect use of water, the use of poor quality water and the use of unsuitable soil. These problems are often interrelated and lead to serious consequinces especially in arid areas. Water may enter the plant root zone either by percolation from above or by a rise in the level of the water table. The former occurs naturally with rain or irrigation. The latter occurs due to over irrigation or to excessive seepage from canals and irrigation ditches. All water, except rain water, contains dissolved chemicals or ‘salts’ and when evaporation or transpiration takes place these salts are left in the ground. If the concentration becomes too great the soil is said to be saline and plant growth may be affected. Irrigation with water con-tainting too high a concentration of salts can quickly causes the soil to become saline. Similarly a rising water table can bring dissolved salts from lower layer of the soil to the surface where they vacuum- late due to evaporation. A farmer who puts on too much water may cause water logging of the soil and poor plant growth due to lack of air. Later, as the soil dries, plants may be affected by salinity.

Once this problem has developed it can only be solved by periodic leaching (washing out) of the salt by allowing water to soak through the root zone and out into drains which carry it off the land. The problem of salinity is most likely to occur in arid areas where leaching by rainfall rarely takes place and the level of salts in soil is naturally high.

Another problem, known as alkalinity, can arise due to the accumulation of excessive quantities of sodium in the soil. This is sometimes, but not always, associated with high salinity.

Excessive sodium can lead to the breakdown of soil structures and the formation of an impervious layer below the surface, which makes irrigation very difficult. Whereas a saline soil can normally be improved by leaching, a soil which is alkaline usually requires the application of gypsum or sulphur which can be expensive.

2.5.3: DRAINAGE

This is the removal of excess water or lowering of water from a marshy water logging land by using constructed open ditches, channels and graded land.

šThe importance of drainage to facilitate leaching and prevent ground water levels rising is often

šoverlooked until crop growth begins to deteriorate.

š Drains can be simply open ditches l—2m deep and spaced from 50~200 m apart depending on the permeability of the soil. Where open ditches would interfere with mechanized farming, it is possible to use underground drain pipes. These are usually made

šof clay or plastic.

Many soils which are normally waterlogged can be developed for growing crops by means of drain- age. In some places the use of open ditches is coupled with camber beds which are simply raised beds to improve surface drainage and allow plants to grow in properly aerated soil. Some countries such as the Netherlands have been able to reclaim vast areas of land, which was formerly under the sea, by means of complex drainage systems, and in East Africa there are many areas which are predominantly swamp, which could become productive if drained.

The control of soil moisture in the root zone of crops, either by irrigation or drainage is one of the main ways in which food production can be in- creased to keep pace with the continent’s increasing population.

THE IMPROVEMENTS ABOUT BY DRAINAGE ARE MANFORD

(Advantages of drainage )

Ä The soil are more easy and sooner worked in spring

Ä When the water is carried away from the surface area of the soil air enters the pore spaces and plant roots extended downward

Ä Beneficial of plant microorganism to participate in plant nutrients

Ä It cause washing action on the soil particles

Ä Field drains are easy to open furrows or ditches

Principles of drainage

NB; except under air condition, rainfall cause water logging that water enters various pore spaces due to the permeability of the soil

ÄThe depth of drains should be with the rate of percolation (type of soil)

Example

Soil depth Interval (in ft)

Clay 2 to 2.5 12 to 20

Medium loam 2.5 to 3 20 to 30

Sandy loam 3 to 4 30 to 40

Petty at least 3.5 18 to 21

Ä The distance between drain should be appropriate with texture of the soil

Ä The objective of drainage is to offer ability to removing water from soil by using minimum costs

Ä The permeability of soil depends on it’s type and it’s size of particles (that is drainage should consider the permeability of the soil )

Ä The distribution of rainfall should be fairly in areas that are being drained.

Ä Drainage should consider grantation of an area,that vertically area(gravity),the drainage is to create great channels but on flat land is to use pipe pumps.

Types of drainage

v Surface drainage

v Sub-surface drainage

Surface Drainage:this is the removal of excess water from the surface land

Sub-surface drainage:this is the removal of excess water from root zone(soil water) that prevent air from getting to plants

Methods of drainage

Ø Use of open ditches

Ø Use of underground drain pipes for clay soil

Ø Pumping out water from the soil

Ø Planting trees specie which absorb a lot of water

Ø Combined beds

Importance of Drainage

Ä It increases soil aeration and structure

Ä It’s important on rising soil temperature

Ä It’s important in increasing microbios activities in the soil

Ä It increase soil volume for easy penetration of roots

Ä It reduce waterbone diseases and toxic from soil

Ä It creates stable water table

Areas to be drained

ØAreas with poor (insufficient slope)

ØImpermeable areas (areas with hard pans)

ØAreas with high rainfall

necta 2018:P1:5(d)Briefly explain six importance at drained irrigated farm.

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PART II Agricultural science (SOIL SCIENCE)

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