In order to investigate the effect of nitrogen (N) fertilizer and transplanting date (TD) on yield, yield components and stem lodging of rice (Oryza sativa), a two-year study (2007-2008) was carried out in Fozveh Research Station, Agricultural and Natural Resources Research Center of Isfahan, Iran, using split plots, based on randomized complete blocks design with three replications. Four N fertilizer levels (control, 126, 180 and 234 kg/ha N) were assigned as the main factor and three TDs (late May, early June and late June) were assigned the sub-factor. The results showed that application of 126 and 180 kg/ha N caused 13 and 17% increase in the yield, respectively, as compared to control. But, the 234 kg/ha N treatment had similar yield to control treatment (6672 kg/ha), due to severe stem lodging (45%). The highest agronomic N efficiency (17.7 kg of grain produced per kg of consumed N) was obtained in the 180 kg/ha N treatment, and this was not significantly different from the 126 kg/ha N treatment. Number of panicles per m2 in 126 and 180 kg/ha N treatments, was increased by 16 and 24%, respectively, over the control treatment. Transplanting the seedlings to the main field in late May and early June produced a yield of 7391 and 7831 kg/ha, respectively. Although the stem lodging in late June was lower than the other two TDs, but grain yield was reduced by 29 and 37% with respect to late May and early June, respectively. The results showed that application of 126 kg/ha N and transplanting the seedlings in late June is recommendable for Sazandegi rice cultivar in Isfahan region.

Keywords: Stem lodging, Agronomic N efficiency.

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