Effects of drainage intensity on water and nitrogen use efficiency and rice grain yield in a semi-arid marshland in Rwanda

Abstract

Drainage management is important in intensification of irrigated paddy rice production. This studyassessed the effects of drainage intensity on water and nitrogen use efficiency and rice grain yield inafield experiment conducted during three seasons in Rwanda. The experiment comprised 12 plotswith four blocks and three treatments: DS0.6(0.6 m deep drain), DD11.2(1.2 m deep drain, controlstructure open four times per week), and DD21.2(1.2 m deep drain, control structure open two timesper week). Outflow was calculated from water balance. Nitrogen (N) content in drainage water wasdetermined weekly. Crop yield and N uptake were determined in grain and straw.In all seasons, grain yield was 61–131% higher, crop N uptake was 24–90% higher, harvest index(HI) was 24–65% higher and water use efficiency (WUE) was 50–150% higher in treatments DD11.2and DD21.2than in DS0.6. There was a decrease in soil carbon/nitrogen ratio at the end of Seasons 2and 3. Recirculating straw tofields is thus necessary to replenish SOC for long-term soil fertility. Apractical implication of the study is that managed deep drainage systems could enhance water useefficiency and rice grain yield in poorly drained paddyfields