Economic evaluation of salinity,drainage and non-uniformity of infiltrated irrigation water

Salinity, drainage and non-uniformity of irrigation water are important components in determining optimal water application and related profitability. A crop-water production function assuming steady state conditions is incorporated in a long-run economic model to investigate the combined effects of salinity, irrigation uniformity and different drainage requirements at the field scale for the specific crop.The analysis was conducted for corn and cotton as sensitive and tolerant crops to salinity, respectively. Optimum applied water and associated profits, yield and drainage volumes were computed for each crop. The computations were done for the condition that no drainage system was required and also where a drainage system was required and the drainage water was disposed of to either a free off-farm facility or to an on-farm evaporation pond constructed on productive or non-productive land.The main findings are that type of drainage disposal system affects the optimal values of applied water, profits, yield and drainage volumes, except for uniform water applications and non-saline irrigation water. Another finding is that in the long run, under saline conditions and/or different drainage disposal systems, a sensitive crop such as corn is not profitable and goes out of production. In general the profit levels associated with the various drainage options are in the order of no drainage requirement ? free off-farm facility > on-farm evaporation pond on non-productive land > on-farm evaporation pond on productive land. Uniformity of irrigation water affects values of the analyzed variables and the effects are greatest for the cases of on-farm evaporation ponds. Pumping cost effects are quite small, but water price effects are more significant. Breeding the crops for increased salinity tolerance has little effect when irrigating with water of low salinity and/or low irrigation uniformity.