Soil fertility is the ability of the soil to provide nutrients in proper quantities and in a balanced way for the growth of plants. A fertile soil should have the correct proportion of plants nutrients and optimum pH
Soil productivity is the capacity
of the soil, in its normal environment to support plant growth
Soil fertile greatly affects soil
productivity. A fertile soil always leads to high soil productivity
However, soil productivity is affected
or influenced y other factors other than the soil fertility. For example,
presence of weeds in the farms may lower the level of productivity of the soil,
even when the soil fertile. Other factors like farming methods used may also
lower the productivity of the soil.
In farming, soil fertility may lost
through many ways, some of these ways are as result of human
activities while others are through natural process.
The following are some
ways through which soil fertility may be lost:
(1) Leaching
This is common with nutrients that are highly
soluble such as nitrogen, these nutrients are carried to lower far from beyond
the reach of many plants roots, soil with many leached nutrients are
infertility.
(2) Soil capping
This is when the soil is covered (capped) with
an impervious material which prevents the penetration of rainwater into the
soil, this leads to surface run – off. This denies the soil adequate moisture
and exposes the soil to erosion
(3) Soil erosion
This is the carrying away of the top fertile
soil by moving water and wind. Erosion leads to loss of the fertile top soil
and plant nutrients, this makes the soil infertility.
(4) Monocropping
Monocropping is the practice of growing one
type of gropes on a piece of land for a long time. The gropes grown uses only
those nutrients it needs while other nutrients remain unused, this leads to
exhaustion of some nutrients and eventually to their deficiency in the
following years
There is also likelihood of build up of pests
and disease, the same pest and disease are passed on from the residue of
previous crop, this leads to low yield
(5) Accumulation of salt
Soil water contains dissolved minerals salts
from the parent rock; some of the salt comes from decomposition of organic
matter.
Under normal condition, the salts are washed away
by rain water, thereby keeping their concentration in the soil low. However in
arid and semi-arid areas the rainfall is irregular and is not enough to remove
the salt from the soil.
This together with the high evaporation rate
and poor drainage, leads to accumulation of salt on or below of the soil
surface. The salt cause deficiency of water in plants as water moves out of the
root in the soil under the osmotic pressure of the salt solution.
(6) Change in the pH
Inappropriate use of fertilizers may change
the soil pH, for example, the use of acidic fertilizer over a long period of
time can make the soil acidic.
Change in pH affects the activity of the soil
microorganisms and the availability of some nutrients. This, in run, affects
the fertility of the soil.
(7) Burning of vegetation
When vegetation is burned, organic matter is
destroyed; this affects the activities of microorganisms such as nitrogen
fixation and decomposition of organic matter.
Accumulation of the resulting ash also causes
imbalance of nutrients in the soil. Burning of vegetation also exposes the soil
to agents of erosion such as wind and water.