Abstract
Exploring approaches to optimizing spatial distributions of leaf area index (LAI) and leaf nitrogen content (LNC) should be useful for increasing grain yield in rice (Oryza sativa). The primary objective of this study was to characterize the variation of LAI and LNC distributions within the canopy in relation to grain yield and N uptake in rice. Two experiments with different N fertilization rates under conventional and intermittent irrigation (CI and II, respectively) were conducted in 2002 and 2003, using Japonica rice cultivar Wuyujing9. The results showed that grain yield and N uptake were significantly different among application rates of N (N rates), but did not differ between CI and II. LAI distribution at full heading was affected significantly by N rate but hardly by the irrigation method. Individual LAI increased with the N rate. To achieve a high yield, the proper distribution of LAI in the canopy can be designed as the largest in the 2nd leaf from the top, followed by the 3rd and 4th leaves, and the smallest in the top leaf. LNC on the base of both area and dry matter at 15 days after full heading decreased from the top to lower leaves in the canopy, and significantly increased with the N rate. Grain yield was enhanced linearly with the increasing N content of the upper two leaves, but hindered by the high N content of lower leaves. These results indicate that the spatial distributions of both LNC and LAI could be optimized to achieve maximum canopy photosynthesis and grain yield in rice.
