Crop water productivity and economic evaluation of drip-irrigated soybeans (Glyxine max L. Merr.)

Abstract

Effective management of water under irrigated agriculture is crucial to ensure food security. One crop that has high irrigation economic potential at local and international scales is soybean. This article presents the outcome of field experiments conducted in the dry seasons of 2013 and 2014 in Nigeria on the effects of deficit irrigation (DI) practices on reproductive stages of soybean. The experimental factor was the timing of irrigation. The five treatments were full irrigation (FI); skipping of irrigation every other week during flowering; pod initiation; seed filling and maturity stages.The crop was planted in a randomized complete block design with three replicates and inline drip irrigation was used to apply water. Leaf area index, dry above-ground biomass and seed yield were measured and the soil water balance approach was used to determine seasonal crop water use. Seasonal crop water use for the treatment in which deficit irrigation was imposed at seed filling stage was 364 mm while for the control treatment with full irrigation, seasonal crop water use was 532 mm. The seed yield reduced by 18.8 and 21.9% when DI was imposed during flowering and pod initiation, respectively. Similarly, the seed yield reduced by 24.4 and 47.9% when DI was imposed during maturity and seed filling. Water productivity (WP) reduced by 6.8 and 12.4% when DI was used during flowering and pod initiation, respectively. However, WP reduced by 20 and 35% during maturity and seed filling. DI during reproductive stages reduced economic water productivity by 6.7–35% while revenue was reduced by 18.5–47.7%. Full irrigation should be practiced to maximize water productivity. Weekly skipping of irrigation during seed filling will substantially reduce the seed yield and water productivity while skipping during flowering may be a viable option when water is scarce and land is not limiting. Economic evaluation will guide policy makers at basin scales for formulating improved and efficient water management plans under all varying weather conditions. DI can be used to optimise water productivity. The results will be beneficial in adopting deficit irrigation in a manner that will improve economic water productivity.