Effects of nitrogen application in upland rice cultivars: Balancing sink-source relationships for sustainable yield in water-limited environments
Nobuhito Sekiya, Akira Asano, Mchuno Alfred Peter, Emily Gichuhi, Daniel Makori Menge, Mayumi Kikuta, Makoto Kondo, Daigo Makihara
Abstract
Nitrogen management is crucial for sustainable production of upland rice in water-limited environments. However, the complex relationships between nitrogen application, water availability, and yield formation in upland rice are not fully understood. This study investigated the effects of nitrogen application rates on yield formation and physiological responses of two upland rice cultivars under different moisture regimes in semi-arid Kenya. Field experiments were conducted over two years using two upland rice cultivars (NERICA1 and Yumenohatamochi) under varying nitrogen application rates (0–150 kg N ha −1 ) and moisture conditions. Yield, yield components, and physiological variables were measured. A non-linear response to nitrogen application was observed, with yields increasing up to 75 kg N ha −1 but decreasing at 150 kg N ha −1 . Nitrogen application significantly interacted with irrigation, with irrigation unexpectedly decreasing yield under excessive nitrogen conditions (150 kg N ha −1 ). Excessive nitrogen application led to preferential allocation of assimilates to vegetative organs at the expense of grain filling, where a part of the assimilates were utilized for structural growth, and the remainder, likely due to the increased sink capacity, accumulated in vegetative organs during grain filling. The cultivars differed significantly in their nitrogen response, with NERICA1 showing greater yield stability across nitrogen levels. Our findings emphasize the importance of optimizing N application rates (around 75 kg N ha −1 in this environment) and cultivar selection for efficient upland rice production in water-limited areas. These results contribute to developing sustainable fertilization strategies for upland rice in semi-arid regions, potentially improving food security. • Upland rice shows non-linear yield response to nitrogen, with a decline at high N rates. • High N diverts assimilates to vegetative growth over grain filling. • Enlarged vegetative organs promote NSC accumulation over grain filling. • Structural growth and NSC accumulation decrease yield under high N and irrigated conditions. • NERICA1 maintains yield stability across N rates compared to YHM.