Effect of irrigation amount and tillage system on yield and water use efficiency of cowpea

Yield, water storage, and water use efficiency of irrigated cowpea ( Vigna unguiculata L. Walp) were evaluated under four tillage systems and five irrigation regimens. The tillage systems are conventional tillage, reduced tillage, zero tillage, and manual tillage, and the irrigation regimens were created by using a line source sprinkler system. Reduced and conventional tillage produced higher yield and water use efficiency than zero and manual tillage (p < 0.05). Reduced tillage produced the highest yield of 1.88 t/ha and had slightly higher yields than conventional tillage in the first four irrigation levels because of higher water storage and lower percolation than conventional tillage. Although manual tillage had high water storage and low percolation, the water was not beneficially used probably because of high evaporation leading to significantly ( p< 0.05) high soil moisture tension before irrigation. Zero tillage, on the other hand, resulted in significantly ( p< 0.05) lower application efficiency due to higher runoff. Therefore, irrigated land requires some forms of mechanical tillage or water conservation measures for manually tilled land for improved water use efficiency.