Effect of nitrogen fertilizer application on grain yield and milling recovery of rice (Oryza sativa cv. Khazar)

To evaluate the effect of application of different levels of nitrogen fertilizer on grain yield and yield components of rice (cv. Khazar), a field experiment was conducted at Rice Research Institute of Iran using a randomized complete block design with 11 treatments and three replications in 2008 cropping season. 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) on fully developed leaf of rice plant. Results showed that the maximum number of tiller.m-2 and tiller fertility was recorded in S40N30 (SPAD40+30 kgN) treatment with 242 tiller.m-2 and 90% tiller fertility. Maximum number of panicle.m-2 was recorded in S38N30 (SPAD38+30 kgN) treatment with 247.33 panicle.m-2, which had not significant difference with other treatments. Mean of highest grain number.panicle-1 (145.17) and maximum panicle fertility (68.51%) was recorded in S40N30 (SPAD40+30 kgN) and S38N30 (SPAD38+30 kgN) treatments, respectively. Highest rate of 1000-grain weight was recorded in S40N30 (SPAD40+30 kgN) treatment (29.60 g), as well as the maximum grain yield with 5559 kg.ha-1. Minimum grain yield was obtained in control treatment (without N) with 3454 kg.ha-1. Maximum milling recovery was also observed in S40N30 (SPAD40+30 kgN) treatment with 68.6% which was 7% higher than the recovery rate in recommended level of fertilizer and 28% greater than control. It can be concluded that splitting of nitrogen fertilizer application at appropriate rate, considering plant requirement, may improve grain yield, yield components and milling recovery in rice.