Altitude,temperature, and N Management effects on yield and yield components of contrasting lowland rice cultivars

Nitrogen (N) is one of the main nutrients that drive rice grain yield and is intensely managed especially in lowlands under irrigated conditions. A set of experiments was conducted in mid- and high-altitude sites in Rwanda to investigate the response of five genotypes under different sowing dates and different N management. Genotype grain yields were higher and more stable at mid-altitude across sowing dates. N rates strongly affected grain yield at mid-altitude (p < .0001), but not at high altitude. Postponing basal N had positive effects on yield and yield components in both sites, with more pronounced effects at high altitude. Increasing N rate beyond 120 kg/ha led to a decrease in percentage of panicles per tiller and spikelet fertility and a decrease in grain yield due to excessive tillers at both high altitude and mid-altitude. Thus, basal N application should be recommended at high altitude and the increase in N rate up to 120 kg/ha at mid-altitude. A strict observation of recommended planting date should be followed at high altitude, and the use of cold-tolerant genotypes is encouraged.