ABSTRACT
The field experiment was conducted during the 2011 dry season at the Irrigation Research Fields of the Institute for Agricultural Research (IAR), Samaru, Nigeria, to evaluate yield and soil water balance of two cowpea varieties under deficit irrigation and mulch using locally assembled weighing- type micro lysimeter. The treatments comprised of three levels of irrigation water application depths (50%, 75% and 100% of weekly reference evapotranspiration (WRETo)) and two levels of mulch (No mulch- NM, and black polyethylene mulch -BPM) and two varieties of cowpea (SAMPEA7 and 9) laid in a group balanced block on split-plot design. The result showed that the yield of the cowpea pods ranged from 0.29 t/ha to 1.29 t/ha. The highest yield was obtained from SAMPEA7 treatment irrigated at 100% WRETo with BPM. The drainage depth ranged from 3.9 mm to 89.5 mm with the least value obtained by SAMPEA9 at 50% WRETo and NM. The highest depth was by SAMPEA9 at 100% WRETo and BPM. In comparison, SAMPEA7 gave less drainage water compared to SAMPEA9. The study showed that crop water use of cowpea ranged from 187.6 mm to 335.6 mm for SAMPEA9 and 191.3 mm to 315.8 mm for SAMPEA7 with the least values occurring at 50% WRETo and NM. The estimated values of Kc for the two cowpea varieties at initial, crop development, mid and late season stage were 0.32, 0.58, 0.63 and 0.39, respectively for SAMPEA7 and 0.32, 0.63, 0.72 and 0.34, respectively, for SAMPEA9 varieties. The highest crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE) were 3.76 kg/ha-mm and 2.11 kg/ha-mm, respectively, for SAMPEA7 variety and 2.94 kg/ha-mm and 1.68 kg/ha-mm, respectively, for SAMPEA9 variety. The crop yield response factor (Ky) was found to be 1.10 for the BPM treatments and 1.22 for the NM treatments. In conclusion, SAMPEA7 variety irrigated at 75% WRETo with BPM gave the highest WUE of 2.11 kg/ha-mm which translates to highest yield per unit depth of water-use.