Combined effects of agro-ecological water and nutrient management practices on yield and water use efficiency in inland valley rice cultivation in South Benin

Abstract We tested several water management practices in interaction with standard fertilization practices on rice systems in the Matekpo inland valley in southern Benin from April to July 2022. Treatments included continuous flooding (CF), soil saturation (SS), alternate wetting and drying to 15 KPa (AWD15) and 30 KPa (AWD30), combined with control fertilization at recommended dose (DR-NPK), micro-dosing of NPK (75% DR-NPK) and agro-ecological based fertilization [compost (5 t/ha dry matter-DM), biochar plus compost(BCO), (5 t/ha DM of biochar + 2.5t t/ha DM compost), rice straw (9 t/ha DM), rice straw plus compost (2.5 t/ha DM compost + 4.5 t/ha DM straw)]. We arranged treatments in a strip-plot design with three replications. We monitored rice plant growth, rice paddy yields at harvest, and water dynamic parameters. We analyzed the collected data in RStudio 2023.06.1. The results show that SS, AWD15, and AWD30 allowed saving 29%, 47%, and 58% of water, respectively compared to CF. In addition, average paddy yields are not significantly different between CF (3.99 t/ha), SS (3.69 t/ha), and AWD15 (3.62 t/ha) but better compared to AWD30 (2.98 t/ha). Moreover, actual evapotranspiration (Eta) is 4.62, 4.88, 5.58, and 6 mm/day in the AWD30, AWD15, SS, and CF treatments, respectively. However, water use efficiency (WUE) is not different among water management practices. Moreover, the interaction with the different fertilizers gives better WUE in AWD30 + RSCO, AW15 (RSCO, CO, BCO), and CF+NPK treatment. In short, mineral fertilizer treatments are more demanding in water, whereas agroecological fertilization treatments show better yield and water efficiency under intermittent irrigation (AWD). In agroecology, the most efficient combinations use less water without compromising yield. Combinations that meet these agroecological principles include moderate alternate wetting and drying combined with organic fertilizers (AWD15 + BCO); AWD15 + RSCO and AWD 15 + CO). Keywords: Agro-ecology, water and nutrient management practices, rice cropping systems, inland-valley, water use efficiency.