LAUSR

Abstract Rice yield can be increased by improving yield potential through breeding and expressing the yield potential by overcoming yield-limiting factors. Nitrogen (N) is the most limiting nutrient for rice growth and yield. In the past 60 years, rice yield and N rate applied have almost increased simultaneously in China. The objective of this study was to test the hypothesis that expressing yield potential by increasing N rates was the major factor responsible for the rice yield increase in China. A five-season field experiment was performed to determine the response of yield attributes to N rate in two elite double-cropped inbred rice cultivars released 41 years apart, i.e., an old cultivar Guangluai 4 released in 1967 and a relatively new cultivar Zhongjiazao 17 released in 2008. Five N rates (i.e., 0, 50, 100, 150, and 200 kg ha–1) were employed for each cultivar. Grain yield of Guangluai 4 was increased with increasing N rate until a peak of 7.59 t ha–1 was reached at an N rate of 178 kg ha–1, while grain yield of Zhongjiazao 17 was increased with increasing N rate within 200 kg ha–1 and was estimated to achieve a maximum value of 7.96 t ha–1 at a N rate of 213 kg ha–1. The response of grain yield was closely related to the responses of panicles per m2 and total biomass in both cultivars. The results suggest that the increased N rate allowed the expression of yield potential by overcoming N limitation and meeting the higher demand of N rate for newly developed cultivars, and hence played an important role in increasing grain yield of double-cropped inbred rice in China over the past six decades. This study also indicates that the contribution of genetic improvement to the yield increase of double-cropped inbred rice in China might be not as great as previously believed.