Pollution of Water Resources from Agricultural Fields and Its Control - Practices of Irrigation and On-farm Water Management - page 266

(iii) Soil nitrate test for N side-/top-dressing requirements : Soil test for N offers
the possibility of reducing the extent of over-fertilizing with N.
(iv) Use of slow-releasing fertilizer : Fertilizers that release N at the slower rate
meet the crop demand and reduce the chance of leaching.
(v) Appropriate method of application (e.g., deep placement, fertigation) :
Fertilizer N can be applied in the irrigation water (fertigation). Side-dress
application for most N fertilizer (in the humid regions or under irrigation in
the drier climate) can reduce the extent of nitrate pollution.
(vi) Accumulation of nitrate in soil by mineralization after harvest should be min-
imized : Cover crops to take up nitrate remaining in the soil at the end of the
growing season can reduce the extent of nitrate pollution.
(vii) Some deficit irrigation ( 40% ) : Some allowable deficit irrigation can reduce

or eliminate percolation, and thus reduce N leaching. Matching irrigation
amount to crop evapotranspiration (ET) will also reduce N loading to the
groundwater.

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7.7.3 Cultural Management/Other Forms of Management

(i) Cover crop : Some amount of solutes (N) remains in the soil at harvest of the
crop. After harvest, where the land remains fallow, if a cover crop is grown, it
will absorb the available nutrients and thus will reduce the chance of leaching.
(ii) Zero tillage/minimum tillage : In some instances, where zero tillage or mini-
mum tillage is possible, it will reduce percolation rate and thereby increase the
opportunity time, which will reduce the leaching of solutes.

Within the state-of-the art, the fertilizer and irrigation application can be altered
to enhance nutrient and water uptake, while minimizing leaching below the root
zone. Thus, appropriate management of nitrogen fertilizer, irrigation, and other
management practices can reduce nitrate leaching to a large extent.

7.8 Models in Estimating Solute Transport from Agricultural
and Other Sources

Nowadays, computer simulation models have become a useful tool in understand-
ing the transport of water and solutes through the soil into the groundwater. Models
are useful tools for integrating different processes involved in nitrogen transport in
soil and can be used in forecasting how a system will behave without actually mak-
ing measurements in the physical system. Models are particularly useful describing
and predicting transport processes, simulating conditions which are economically
or technically impossible to carry out by field experiments.
Some of the available & commonly used models for NO 3 -N leaching are as
follows: