Evaluation of crop yield models for cowpea in Nigeria

Three phasic models namely, Hanks (H-2), Stewart (S-2) and the Hall–Butcher (H–B), were evaluated on cowpea irrigated using a line source sprinkler system. Three sets of field data (1983, 1985, and 1986) were collected; the 1985 data were used for calibration while the 1983 and 1986 data were used for evaluation of the models. The model performance that most accurately matched the measured data was then used to simulate the most water-efficient irrigation schedule and deficit irrigation analysis for cowpea in Nigeria. Results showed that the models gave good estimates of cowpea grain yield with the H-2 model performing slightly better than the other two models. The weighted root mean square deviations were 0.043, 0.094, and 0.213 for the H-2, S-2 and the H–B model, respectively. Simulation studies with the H-2 model showed that irrigating at 40% moisture depletion is the most water-efficient schedule for cowpea and that greater yield from a given optimum seasonal water application for deficit irrigation can be achieved by splitting the seasonal deficit among the growth stages.