Saving Water in Paddy Rice Fields under the System of Rice Intensification in Uganda.

Abstract

The extent of water wastage to furnish inefficient irrigation systems especially in flood irrigated rice systems in Uganda, is not known. Too much water not only compromises nutrient use efficiency, but has also been associated with the spread of water snail (Pomacea canaliculate), a pest that eats up young rice seedlings and transmits bilharzia (schistosomiasis). System of Rice Intensification (SRI) has been found to reduce greenhouse gas emissions, water and nutrient wastage; it also increases rice yields, though its benefits in flooded rice systems in Uganda have not been fully been explored. The overall objective of this study was to optimize water use efficiency (WUE) under SRI in flood irrigated systems in Uganda. The specific objectives were to: (i) establish the minimum flooding depth for optimal WUE and grain yields (ii) determine the effect of spacing and seedling rate on rice growth parameters, grain yield and WUE and (iii) determine the effect of seedling age at transplanting on rice growth parameters, grain yield and WUE. Field experiments were established for two seasons (December 2021– March 2022 and May - Sep 2022) in Doho Rice Irrigation Scheme (DRIS) in eastern Uganda. The main treatments included four flooding depths (0mm / Field Capacity, 10 mm, 20mm and 40mm) and within each flooding depth, were split plots that included (i) the number of seedlings per hill (1 or 3) and (ii) spacing (0.20 m x 0. 20 m or 0.25 m x 0.25 m). Crop parameters measured included plant height, number of tillers, number of panicles, shoot and root biomass and grain yields. There were no significant differences in biomass and grain yields among the four flooding depths. WUE was 16.5 ± 0.2kg/mm/ha under field capacity, which was significantly higher than the 3.1kg/mm/ha under the 40 mm ponding depth. This is a clear indication that paddy rice can be produced under soil kept at field capacity. Planting one seedling per hill at a spacing of 0.25m x 0.25m led to a higher number of tillers, panicles and consequently biomass and grain yields than three seedlings per hill, implying that farmers practice of up to six seedlings per hill not only wastes seed but suppresses yields. Seedling age at planting had a significant effect on both grain yield and WUE. Higher grain yield (4.6 ± 0.2 t/ha) and WUE (8.9 ± 1.2 kg/mm/ha) were from seedlings transplanted at 14 Days After Emergence (DAE) compared to grain yield (1.9 ± 0.2 t/ha) and WUE (0.8 ± 0.1 kg/ha/mm) obtained from seedlings transplanted at 30 DAEs. It can be concluded that ponding of up to maximum of 10 mm of water every three days and transplanting of 14 DAEs seedlings of 1 seedling per hole at a spacing 0.25m x 0.25m leads to optimum WUE and increased rice grain yields. This can save up to 33% of the water farmers use to grow rice.