Effects of nitrogen uptake on rice yield in northern Australia

Summary The yield responses to nitrogen uptake are described for water-sown IR8 rice grown in the wet season in northern Australia. Various patterns of nitrogen uptake were achieved by different times and amounts of nitrogen application in the range 0 to 300 kg per ha. Grain yields increased with nitrogen uptake at flowering stage up to approximately 120 kg per ha but decreased when uptake exceeded this level. The grain yield increase was associated mainly with increased panicle production, while grain yield decrease was associated with a reduction in the weight of ripened grain per panicle. Nitrogen concentration in grain over all experiments increased linearly with nitrogen uptake at flowering, but grain yield was reduced when grain nitrogen exceeded approximately 1.5 per cent. High nitrogen uptake at flowering was presumed to lead to depletion of carbohydrate reserves during the critical grain-ripening phase.