PLANNING LENGTH OF LONG -TERM FIELD EXPERIMENTS THROUGH DECISION SUPPORT SYSTEMS – A CASE STUDY

Abstract

Long-term field experiments are the conventional means for developing; evaluating and demonstrating site-specific land/water use plans. However, it has been often observed that at times they are unable to propose sustainable practices, when planned for shorter time durations (say 2-3 years) or become cost-ineffective and obsolete, when planned for longer time durations (say more than 15 years or so). Hence, what should be the ideal length of such long-term experiments has always been a debatable issue. The present study attempts to demonstrate application of one indigenously developed decision support system (DSS) for planning appropriate length of long term conjunctive water use experiments on a test salt affected farmer’s field. Before application the proposed DSS was extensively validated on several farmers and controlled experimental fields in Haryana (India). Validation of DSS showed its potential to give realistic estimates of root zone soil salinity; sodicity and salt stress induced relative crop yield reductions under local resource management conditions. Long term impact assessment of varied conjunctive water use strategies, on the test farmer’s field, with the so validated DSS showed that the time required for achieving stable crop yields could be treated as a good measure of the minimum length of such experiments. For the test (rice-wheat growing) farmer’s field, this time ranged between 5.5 – 6.0 years. It was observed that at shorter time scale (i.e. 2 years), though application of 50% canal waters (CW) blended with 50% tube well waters (TW), was as productive and superior as cyclic applications of (2CW, 1TW, 1CW); (1CW, 1TW, 2CW) and (CW: TW) during wheat cropping season yet it could not maintain its superior performance at DSS proposed time duration of 6 years or more. Similarly irrigation practice of (4CW, 5TW) during rice cropping season, though beneficial at shorter time scale, was much inferior to the cyclic application of canal and tube well waters (i.e. CW: TW) at longer time scales (i.e. at ≥ 6 years). Hence, limiting the proposed long-term conjunctive water use experiment to the DSS proposed minimum time duration of 6 years lead to the selection of the most stable and sustainable irrigation practice(s) for the test farm.