Cowpea yield response under alternative irrigation scheduling techniques using line-source sprinklers

A portable hand-move sprinkler irrigation system was designed to provide water distribution and operating characteristics suitable for continuous variable irrigation-fertilizer cowpea (Vigna unguiculata [L.] Walp.) production studies. Both the single and interactive effects of irrigation water, phosphate fertilizer and irrigation scheduling techniques on cowpea dry matter production were investigated in a field-conducted randomised complete block experiment. The relative merits of irrigating frequently but with smaller amounts of water than the design water application depth as compared to stage-of-growth and normal interval irrigation were studied with five levels of fertilizer P and three water levels. Soil water depletion by crop was measured by gravimetric methods and water use as well as water use efficiency were subsequently evaluated. Plant growth rate indices monitored were: plant height, number of trifoliates and number of nodes on a weekly basis for seven weeks following emergence. Statistical analyses of yield and P uptake indicated positive response of the crop to added fertilizer and irrigation water, most noticeably under the high-frequency schedules. Water use efficiency was observed to be highest under the most frequently-irrigated plot(S3) but this happened to be obtained at the expense of depressed yields. It was therefore concluded that irrigating twice within the designed interval was optimum for both yield and water use efficiency considerations. The line-source irrigation system and experimental design used in this project were found to be satisfactory for field study of the interactive effects of these test factors on the crop. One major difficulty encountered with running the experiment was the operation of the system under calm wind conditions to ensure high uniformity of water distributiion. Special care was needed also, to achieve sediment exclusion from the lateral that was frequently uncoupled and moved from plot to plot, but these were the special features of the irrigation system that made working with it interesting.Land and Food Systems, Faculty ofGraduat