SOIL FERTILITY AND PRODUCTIVITY IN AGRIC

Notes to be read. Very important

1. Soil fertility :
It is the inherent capacity of soil to supply
nutrients to plants in adequate quantities and in
suitable proportions.
Soil productivity:
It is the capacity of soil to produce crops with
specific systems of management and is
experienced in terms of yield.

2. All productive soils are fertile but all
fertile soils need not be productive.
It may be due to some problems such
as water logging, saline or alkaline
conditions , adverse climate etc.

3. DIFFERENCES BETWEEN SOIL
FERTILITY AND PRODUCTIVITY

4. Features of good soli management:
The interaction of growth enhancing factors that
make a soil productive is referred to as “Soil
quality”.
The maintenance or restoration of soil quality is
highly dependent on organic matter and an
array of beneficial microbes and micro
organisms that it supports.
Proper and regular addition of organic
amendments like animal manures and crop
residues can effectively offset many of these
degradative processes.

5. Soil degradation
processes
• soil erosion
•Nutrient run off
•Water loggging
•Desertification
•Compaction
•Crusting
•Organic matter loss
•Salinization
•Nutrient depletion by
leaching.
•Toxicant accumilation
Soil productivity
Soil conservation
practices
•Conservation tillage
•Crop rotations
•Improved drainage
•Residue management
•Water conservation
•Terrasing
•Contour farming
•Chemical fertilisers
•Organic fertilizers
•Improved nutrient cycling
•Improved systems to match
soil cultivars and climate.
Relatioship of soil degradative processes and soil conservation
practices (Hornick and parr, 1987)

6. The Soil Science Society of America (SSSA 1984)
defines soil quality as an inherent attribute of a soil
which is inferred from soil characteristics or indirect
observations (compactibility, erodibility,and
fertility ).
Thus, soil quality has traditionally focussed on, and
has been equated with, soil productivity.

7. Soil quality might be defined as the capacity or
capability of a soil to produce safe and nutritious crops
in a sustained manner over a long term and to enhance
human health and animal health, without impairing the
natural resource base or adversely affecting the
environment ( Parr et al 1992 )

8. If properly characterised , soil quality should serve as
a measure or indicator of changes in the soil’s
capacity to produce optimum levels of safe and
nutritious food and its structural and biological
integrity , which can relate to the status of the certain
degradative processes, as well as environmental and
biological plant stresses.
Soil quality can decline through all of the
degradative
processes that are cited in the Figure 7.2.

9. Thus, soil quality is directly related to the state of
soil degradation which can also be defined as the
time rate of change in soil quality (Parr et al 1992)
The maintenance or restoration of soil quality is
highly dependent on organic matter and array of
beneficial macroorganisms and microorganisms that
it supports.

10. Proper and regular addition of organic amendments
such as animal manures and crop residues can
effectively offset many of these degradative
processes.
 It is also the best and most expedient means of
developing a biologically active soil that requires
little energy for producing crops, increase in
resistance of plants to pests and diseases ,and
enhance the decomposition of toxic substances
such as residual pesticides (Sampson 1981,
Hornick and Parr 1987 )

11. Good soil- 50 % equal micro and macro pore
spaces.
Porosity= ( 1- BD/ PD)* 100
So the distribution between macro & micro pore
spaces is very important.
More micro pore spaces means more
conductance & more WHC.

12. Addition of organic matter leads to
Better structural strength, encourage microbial
activity ( microbiota), increase BD, no change in
PD.
BD= W/ V
High in loose soil.
Proper irrigation :
Maintaining soils at optimum moisture content
and minimum of air filled porosity.
Soil inherent capacity- oxidation and reduction
p
H
: neutral p
H
is better. Add lime or gypsum.
Crops and crop sequencing.
Reclamation of soils with green manuring.

13. Problems of supply and availability of nutrients
in soil:
p
H :
High H conc favours weathering of minerals resluting
into release of various ions like K
+
,Mn
+2
,Cu
+2
and Al
+3
The solubility of salts like CO
-
3 , PO
-
4 and SO
4
-
is
higher in lower p
H range.
low condition favours the reduction of Fe
+3
& Mn
+2
to
Fe
+2
and Mn
+
respectively.
So the levels of Fe and Mn ions become more in acid
solis.

14. Mo availability is in acidic soils and others are
less.
P is fixed at low are high p
H
.
Problem of supply and availability of N is limited
in soils dumped with huge qty of OM. With wider
C: N ratio.
In such soils N deficiency occurs due to
immobilization because bacterial activity gets
deactivated and N depression takes place.

15. •In soils not containing calcite ,dolomite or gypsum , the amount
of calcium in the soil Solution is dependent on the amount of
exchangeable calcium present
• soil factors of the greatest importance in determinig the
availabulity of ca to plants are the following
• 1.total ca suply
• 2.%ca saturation of soil colloids
• 3.ph
• 4.cec
• 5.type of soil colloids
• 6.ratio of ca to other cations in soil solution

16. •Total ca supply in very sandy acid soils with low cec can be too
low to
Provide sufficient available ca to crops
•High H+ activity occuring at low soil ph will impeed ca
uptake,root
Growth
•In acid mineral soils ,ca is not readily available to plants at low
base saturation (cec)
•Most crops respond to ca when degree of ca saturation is
indicative
Of a favourable ph for growth of most plants

17. Types of clay influences the degree of ca availabulity:
• 2:1 require higher degree of saturation for a given level of
plant utilisation than 1:1 clay
• montmorillite clays require a ca saturation 70% or more
before ca is released sufficiently rapidly to growing plants
• but kaolinate clays are able to satisfy the ca requirtements of
mo0st plants at saturation value & only 40-50%

18. •Ca availability is to uptake by plants is also influenced by ratio
between ca and other Cations in the soil solution
• ca/total cation ratio of 0.10-0.15 is desirable for development
of cotton roots
•Form of inorganic nitrogen :while ca+2 uptake is depressed by
NH+4,
K+,Mg+2,Al+3 its absorption is increased when plants are
supplied with NO3-N