Irrigation water quality and farm management decisions

The quantity and quality of water available for irrigation is variable from place to place in India. There are regions where the farmers have no access to any surface water body nor do they have any ground water source yielding a quality of water acceptable for irrigation use. In some of the coastal areas, neither surface water nor ground water of acceptable quality may be available. On such areas, setting up of an industry and transport of good quality surface water from long distances to the site may be useful for farmers on the adjacent areas; the treated wastewater from the industry may constitute a dependable source for irrigation. This paper gives a brief account of some of these peculiar situations. Whatever be the situation, it is necessary that the water used for irrigation is of an acceptable quality for the crop concerned, growing on the soil of the site. For a given crop, during its growth cycle, it is essential that the concentration of the soil solution around the root zone with regard to dissolved solids and specific ions, does not exceed the tolerance limit for the crop. The tolerance limits for various crops are different, representing 8 to 10 fold variation. Soil type and meteorological parameters of the place, for a given irrigation scheduling, also govern as to what will be the maximum soil solution concentration during the growth cycle of the crop. For a given crop, given soil and prevailing climate, the quality of irrigation water and management ultimately determine this maximum level. At a given place, the type of sail and meteorological parameters cannot be managed by human beings. The farmer can, however, exercise some control on the quality of irrigation water by selecting an appropriate source or changing the quality by dilution or/and he can make certain changes in the agronomic control and crop selection. In this paper, an attempt has been made to describe a few more important irrigation water quality criteria which will be easy for the users to follow and arrive at decision on management, agronomic controls including crop selection and search for an alternative water source of acceptable quality. This paper also describes a few cases of application of the irrigation water quality criteria helping relevant decisions. Judicious use of irrigation water is also necessary even where the water is of an acceptable quality. Excessive irrigation in the command areas under canal;water use is an example where a good quality irrigation water used in a mismanaged way, can cause salinity/alkalinity problems. Good management is a must and this point has also been emphasised in this paper. Proper evaluation of the irrigation water quality, good agronomic controls and management will have long range positive effects on soil and water conservation, optimization of crop yields and stability in the agricultural ecosystem.