Validation of EXNUT for Scheduling Peanut Irrigation in North Carolina¹

During crop years 1989-1992 EXNUT concepts and a version of EXNUT modified for North Carolina conditions were evaluated. This version was revised and evaluated on 20-25 peanut fields during crop years 1993, 1994, 1995, 1996, and 1997 when average yields of 4360, 4890, 4640, 4530, and 4770 kg/ha, respectively, were obtained. These yields averaged 880 kg/ha higher than average yields produced on these irrigated fields prior to 1993 and 1660 kg/ha higher than the average county yields during 1993-1997. The farmers and county agents reported that irrigation scheduled by EXNUT provided an estimated 500 kg/ha increase in yields. Costs of running EXNUT were estimated at $5.14/ha. Using these estimates, net returns from using EXNUT instead of normal irrigation scheduling by the farmer was $272.76/ha. Average compliance of farmers with EXNUT water scheduling recommendations was 85 and 75% for wet years (1994 and 1996) and dry years (1993, 1995, and 1997), respectively. On the average, a 71% or higher compliance with EXNUT recommendations on fields with sandy- and medium-type soils resulted in yields greater than 4480 kg/ha, making irrigation of peanuts feasible in these fields at a world market price as low as $350 per metric ton. Every percentage point increase in compliance with EXNUT recommendations on these fields resulted in an increase in yield of 50 and 110 kg/ha during wet and dry years, respectively. Yields from fields with heavy type soils averaged only 3850 kg/ha because of excessive disease and harvest losses. On the average, peanuts can be produced on this heavy-type soil at world market prices of $410/metric ton if compliance with EXNUT recommendations is at least 80%. This 9-yr study is an example of how expert systems can be transferred through cooperation of researchers, extension specialists, and users.