Nitrogen consumption of double-season hybrid rice and influence factors in South China

Nitrogen consumption(CN),i.e.grams of nitrogen absorbed by plant for producing 1 kg grain yield,is one of the key parameters in determining fertilizer-N rate.The objectives of this paper were: 1) to investigate the CN for early and late season rice in south China;and 2) to evaluate the effects of N rate,timing and climatic factors such as light and temperature on CN.Seven field experiments were conducted during 2001-2005 and CN of double-season hybrid rice in South China was evaluated.The results showed that: 1) CN was significantly affected by fertilizer-N rate and timing.CN increased as N rate increased.Applying N during panicle initiation and grain filling stage resulted in significantly greater CN,while N applied as basal or during tillering had little effect on CN.2) There was a quadratic relationship between grain yield and CN,with an optimum CN at a certain condition.Optimum CN is positively related with sunshine hours during grain-filling stage.Low optimum CN resulted mainly from the low light intensity during grain-filling for early season rice.3) Based on the results obtained in this study and those in the literature,the average CN was 19 and 21 for early and late season hybrid rice for normal years in south China,respectively.The CN parameter can be improved using target yield or sunshine hours during grain-filling stage.