2. Reasons for decline in soil fertility
Soil fertility is a component of overall soil
productivity that deals with its available
nutrient status, and its ability to provide
nutrients out of its own reserves and
through external applications for crop
production.
Introduction
3. 1. Loss of top soil by erosion
2. Nutrient mining
3. Physical degradation of soil (poor structure, compaction,
crusting and waterlogging etc.
4. Decrease in organic matter content and soil bioactivity
5. Loss of nutrients through various routes
6. Soil acidification, salinization and alkalinization
7. Inefficient soil management
8. Soil pollution
Reasons for decline in soil fertility
Causes of decline in soil fertility
4. 1. Loss of top soil by erosion
The top soil is rich in nutrients and organic
matter. Loss of the fertile topsoil components
through erosion by water and wind results in
decreased fertility.
Soil erosion is very common in many parts of
the country.
The basic causes of soil erosion are the result
of human activities such as deforestation,
overgrazing and poor soil management.
Reasons for decline in soil fertility
5.
6. Erosion is the movement of weathered rocks
and soil particles from one place to another.
7. THERE ARE FIVE AGENTS
OF EROSION.
GRAVITY
GLACIERS
WIND
WATER
WAVES
17. WIND
Wind moves soil by
DEFLATION
where wind removes
loose material from
the land.
Here smaller sand grains are blown
away from around larger rocks.
18. WATER
Running water is the
major cause of
erosion.
Water picks up and
carries loose
particles of soil as it
moves downhill.
26. 2. Nutrient mining
Nutrient mining is accelerated by
imbalanced fertilization.
Removal of more nutrients by crops than
added through manures or fertilizers is
called as nutrient mining or depletion.
It is a widespread problem in
low- and medium input
agriculture.
At present, nutrient mining is a
major threat to productive
sustainable farming.
Reasons for decline in soil fertility
27. 3. Physical degradation of soil
High disturbance of soils (tillage) often results
in some structural deterioration, which can be
reversed to different degrees.
Physical degradation of soil (poor structure,
compaction, crusting and waterlogging)
reduces soil fertility.
Soil structure is a variable soil property that,
from an agronomic point of view, can
improve or deteriorate.
Reasons for decline in soil fertility
28. 2. Nutrient mining
The problem is more acute in
areas where high yielding
varieties of crops are being
cultivated
Reasons for decline in soil fertility
It results in the exhaustion of any
nutrient required in moderate to
large amounts.
Nutrient mining could be severe
in the case of N, P, K and S
depending on soil nutrient
reserves and the amounts
replenished.
29. 3. Physical degradation of soil
Waterlogging causes loss of N
through denitrification of
nitrate.
Figure (on the left)
(a) Root growth in a soil with no
mechanical impedance problems
(b) Root growth in a soil with
mechanical impedance problems
Soil compaction decreases the number
of large pores (> 100 μm) and, as these
are the ones through which roots grow
most easily, compaction can have an
adverse effect on root growth (see
Figure).
Reasons for decline in soil fertility
30.
31. 4. Decrease in organic matter content and soil bioactivity
The microbial activities in soil decrease due to
reduced levels of organic matter. These
microbial activities play significant role in
nutrient availability and recycling.
The decreased levels of organic matter
causes a strong reduction in soil fertility
as it plays several roles in soil.
Decreased organic matter levels results
in poor physical , chemical and
biological properties.
Reasons for decline in soil fertility
32. 5. Loss of nutrients through various routes
Nutrient removal by crop products
compared with external nutrient inputs can
be similar, higher or lower. Negative
nutrient balances result where nutrient
removals exceed nutrient additions.
Losses of nutrients from soil can be
caused by soil erosion, leaching, crop
removal or in the form of gases (as in
case of N and to a lesser extent S).
Reasons for decline in soil fertility
33. 5. Loss of nutrients through various routes
Ammonia volatilization from urea and
some ammonium-containing fertilizers
results in losses of nitrogen from soil.
Excessive rainfall, or excessive
irrigation, resulting in the passage of
water through the soil profile through
deep percolation will carry with it
soluble nutrients, particularly nitrate,
sulphate and boron, etc.
Waterlogging causes loss of N
through denitrification of nitrates.
Reasons for decline in soil fertility
34. Picture: Losses of nutrients through different routes from soil
Source: http://wattsupwiththat.com/2009/10/12/fixing-the-nitrogen-cycle-in-climate-modeling/
Reasons for decline in soil fertility
35. 6. Soil acidification, salinization and alkalinization
Factors responsible for soil degradation
are generally interrelated.
Iron deficiency in rice at
higher soil pH
Acidification, salinization or
alkalinization causes reduction in soil
fertility, and eventually lead to problems
of nutrient deficiencies, toxicities and
imbalances.
Reasons for decline in soil fertility
36. 7. Inefficient soil management
Excessive soil tillage leads to erosion of
the soil, which leads to reduced soil
fertility.
Poor or inefficient soil management
results in decreased soil fertility.
Improper crop rotations followed
may decrease the soil fertility
tremendously.
Reasons for decline in soil fertility
37. 8. Soil pollution
The growth of useful soil
organisms is adversely affected,
which eventually causes a decline
in biological soil fertility.
Soil pollution caused by
indiscriminate use of agro-chemicals
and heavy metals reduces fertility of
soil by affecting the soil biological
properties.
Reasons for decline in soil fertility
