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 acces s to any surface water body, nor do they have any ground water source yield ing water of acceptable quality for irrigation. In some of the coastal area s, neither surface water nor ground water of acceptable quality may be avai lable. In such areas, setting up an industry and transporting good quality surface water from long distances to the site may be useful for farmers in the adjacent areas; the treated wastewater from the industry may constitute a dependable source for irrigation. This paper gives a brief account of so me of these peculiar situations. Whatever 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 t he concentration of the soil solution around the root zone with regard to d issolved solids and specific ions, does not exceed the tolerance limit for the crop. The tolerance limits for various crops are different, representin g 8- to 10-fold variation. Soil type and meteorological parameters of the s ite, for a given irrigation scheduling, also govern as to what will be the maximum soil solution concentration during the growth cycle of the crop. Fo r a given crop, given soil and prevailing climate, the qualify of irrigatio n water and management ultimately determine this maximum level. At a given place, the type of soil 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 qua lity by dilution and/or he can make certain changes in the agronomic contro l 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 fo r the users to follow and arrive at a decision on management, agronomic con trols 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 in helping to make relevant decis ions. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.