Mitigation of nitrogen loss in rice fields through soil desaturation prior to re-irrigation and the application of controlled-release nitrogen fertilizer: a meta-analysis

Water pollution by nitrogen residues from agricultural intensification has become a recurring problem, particularly in wetlands used for rice production. As a solution to remediate this issue, sustainable water and nutrient management are being explored. These practices involve matching water and nutrient availability with plant needs in space and time while ensuring production objectives are met. In this study, we performed a meta-analysis to synthesize the current knowledge on the effect of water and nutrient management practices on nitrogen losses and uptake by plants in rice cropping systems. Using a random effects model, we summarized the effect sizes of 103 observations from 27 peer-reviewed studies. Tree water management practices were evaluated: “Continuous Flooding” (used as control), “Alternate Wet and Dry (AWD)” and “Controlled Irrigation (CI)”. The response ratio (RR) of nitrate leaching and total nitrogen loss was negative for CI (-0.53 and -0.34, respectively) and AWD (-0.13 and -0.36, respectively). Regardless of water management practices (AWD or CI), desaturating the soil before re-irrigation reduced nitrate and total nitrogen losses. When considering the source of nitrogen input, water management practices involving desaturation of the soil before re-irrigating were effective in reducing nitrogen losses in urea-only applications. However, in the case of controlled release urea (CRF) applications, water management treatments (AWD or CI) were not necessary to reduce nitrogen losses, especially those due to ammonia volatilization. This result also indicates the effectiveness of CRF treatment in retaining the essential nitrogen component required for plant growth and development. Nevertheless, when nitrogen rates exceed 200 kg N/ha, adopting water management practices such as CI and AWD becomes necessary to decrease nitrate leaching and total nitrogen loss in rice fields. Regarding the rice grain yield, water management practices that involve reducing the amount of water (AWD and CI) have shown no significant effect on yield (RR 0.017 and -0.0001). In conclusion, AWD and CI water management practices have been shown to reduce nitrogen losses without compromising rice grain yield. Additionally, the application of CRF reduces nitrogen losses that may occur in a continuous flooding system.

Key-words: Water management; Nitrogen; Rice; Controlled release urea; Water pollution