Effects of Split Application and Levels of Nitrogen Fertilizer on Growth Indices and Grain Yield of Rice (Oryza sativa Cv. Khazar)

In order to evaluate the effects of nitrogen levels and its split application on growth indices and their relationship with grain yield of rice (cv. Khazar), a field experiment was conducted at Rice Research Institute of Iran with 11 treatments arranged in a randomized complete block design with 3 replications in 2008. Nitrogen fertilizer levels (10, 20 and 30 kg.ha-1) were applied according to three chlorophyll meter (SPAD-502 reading thresholds) (36, 38 and 40) of fully developed leaf of rice plant. Results showed that in S38N30 (SPAD38+30 kgN) and S40N30 (SPAD40+30 kgN) treatments which were received maximum rate of nitrogen fertilizer (103 kgN.ha-1), maximum LAI (3.13 and 3.28) and CGR (29.86 and 29.34 g.m-2) were observed and in S40N30 treatment maximum LAD (1392.86 cm2.day-1) was observed. Analysis of regression showed that there was a significant linear relationship between grain yield and CGR (r2= 0.87**), LAI (r2= 0.88**) and LAD (r2= 0.76**). Maximum grain yield and nitrogen agronomic efficiency (5955 kg.ha-1 and 23.5 kg.kg-1, respectively) were also observed in S40N30 treatment. It seems that the main reason of increasing grain yield in this treatment was improvement of growth indices (CGR, LAI and LAD, respectively) and effective consumption of nitrogen fertilizer. Considering higher grain yield and nitrogen use efficiency in this treatment, it seems that split application of nitrogen in proper rate according to plant demand, may economize nitrogen fertilizer and prevent of its losses in rice production.