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
(c)
Living organism especially vegetable
(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 |
Air |
Determine type of vegetation
CLIMATE |
SOIL |
H2O
from Underground |
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.
Or
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.
(c)
Oxidant: This
is the change of ferrous to ferric compounds.
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
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?
Or
-
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
The separation of soil seen clearly as
it’s classified bellow, ;the decantation process consider duration percentages
|
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
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
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
PD
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)
PD
= 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
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.
OR
-
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.
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
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
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
Ca
Equiv.
wt = molecular wt
Valency
40/2 = 20
Mill
equivalent = mg
Equv. Wt
30= mg
20
= 600mg
Find mg, K and H.
%BS
=
C.E.C
%BS
= E.C – (
C.E.C
=
(30 + 16 + 4) - 4
55
=
51
55
%
BS = 92.75%
Example
2: A soil sample of 20g was analyzed and found to contain 0.0015 of
Solution
Calculate
the equivalent wt of calcium
Equiv.
wt = molecular wt
Valency
40/2
= 20g
1
equiv. wt of
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
EXMPLE 3:
A
soil sample has a cation exchange capacity of 25me/100g; 20g of soil were
shaken with
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
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
= 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 =
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.
Or
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-, H2PO42-,
SO42- 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:-
-
Bacteria that oxidize Nitrite to nitrate
include:-
Nitrobacter
and Nitrocystis
The
process is summarized as follows
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:
- 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.
(C) ADDITION OF MATERIALS CONTAINING PLANT
NUTRIENTS IN ACONCENTRATED FORM
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.
(c)
Calcium ammonium nitrate (CAN)
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)
A
KN03 = 4
x 100 = 14%
39+14+48
Amount = (100 x 80kg)
14
= 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
21
= 286kg
ii). SSP
15P205 = 30kgP205
100P205 = x
100 x 30
15
SSP = 200kg
iii) Muriate
of potash.
Kcl = 60k20
60k20 =
40K20
100K20
= x
100 x40
60
= 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.
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
|
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.
The importance of drainage to facilitate
leaching and prevent ground water levels rising is often
overlooked until crop growth begins to
deteriorate.
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
of 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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