Agriculture Reference
In-Depth Information
is achieved because the trash layer insulates the soil and consequently reduces
evaporation. The trash layer also decreases water runoff which increases deep
percolation.
8.6.2.3 Engineering Practices
There are several engineering approaches to mitigate salinity hazard and facilitate
crop production. These include leaching, drainage, artificial recharge through tube
well (known as “recharge well”), harvesting rain water at farm ponds and canals,
etc.
(A) Leaching
Leaching consists of applying enough good quality water to thoroughly leach
excess salts from the soil. Leaching is accomplished on a limited basis at key times
(saline sensitive stages of crop) during the growing season, particularly when a
grower may have high quality water available. There are two ways to manage saline
soils using this approach:
(i) First, salts can be moved below the root zone by applying more water than the
plant needs. This method is called the leaching requirement method.
(ii) The second method, where shallow water tables limit the use of leaching, com-
bine the leaching requirement method with artificial drainage (Leaching plus
artificial drainage). For proper management of salinity problem, the irrigator
should monitor both the soil and irrigation water salinity.
For leaching, water should be added in sequential applications, allowing time for
the soil to drain after each application. The quantity of water necessary for leaching
varies with initial salt level, desired salt level, irrigation water salinity, and how the
water is applied.
Calculation of Leaching Requirement
The fraction of applied or irrigation water which passes through the root zone
is termed as leaching fraction (LF). Sometimes it is expressed as the percent
of additional water needed above crop water requirements to wash out the salt.
Mathematically, it can be expressed as
D
d
D
i
LF
=
(8.6)
where
D
d
=
depth of drainage water (cm)
D
i
=
depth of infiltrated or irrigated water (cm)
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