The relation between some growth parameters and yield components of rice as influenced by nitrogen level and genotype

Abstract

SUMMARYThe effects of three levels of nitrogen (0, 2 and 4 g (NH4)2SO4 per pot) were evaluated in four rice varieties, differing in grain size, under flooded conditions in a tropical environment.Addition of nitrogen increased plant height and leaf number on the main culm, and hastened flowering significantly in all varieties. It also increased the dry weights of leaf, and culm plus sheath at the maximum tillering stage, anthesis and harvest. The average dry weights of both leaf, and culm plus sheath increased significantly in all varieties until anthesis. Following anthesis, the dry weights of both leaf, and culm plus sheath of the large‐seeded varieties, Zhu Lian and PP6R, further increased mainly due to emergence of the late tillers, but decreased in the small‐seeded varieties, IR 747 and P3C26. During grain‐filling, vars Zhu Lian and PP6R accumulated dry matter more than the other two varieties and did not use their reserve starch present in the culm plus sheath, presumably because of the lack of demand. By contrast, current photosynthesis and ‘reserve’ contributed about 70% and 30%, respectively, of the grain yield in IR 747 and P3C26.Addition of nitrogen increased grain yield significantly in all varieties. The yield increase in IR 747 and PP6R was essentially due to increase in grain number, but that in P3C26 and Zhu Lian was due to increases in both grain size and grain number, the latter having much greater influence. Neither the percentage of filled spikelets nor the 1000‐grain weight was influenced by nitrogen addition. It was concluded that grain number is the single most important yield component in rice. Path‐coefficient analysis indicated that in a breeding programme involving these four rice varieties, the cross between Zhu Lian and P3C26 would be most successful in an effort to combine high spikelet number and large grain size.