Effect of crop rotation, Azotobacter chroococcum inoculation and nitrogen rate on rice (Oryza sativa L.) paddy yield

A considerable portion of chemical N fertilizer in rice field is lost through denitrification, volatilization, leaching, causing environmental pollution problems. It seems that incorporation of winter legume crops in rotation with rice and using plant growth-promoting rhizobacteria can be alternative approaches in reducing N chemical fertilizer and increasing sustainable crop production in rice fields. This experiment was conducted at Rice Research Station of Tonekabon, Mazandaran province, during growing season of 2013-2014 to evaluate the effect of crop rotation, Azotobacter chroococcum inoculation and N rates on rice (Oryza sativa L. cv. Shiroudi) paddy yield.
The experiment was conducted as split-factorial arrangement based on a Randomized Complete Blocks with three replications. Main plots were crop rotation [berseem clover - rice, faba bean- rice, and fallow – rice (control)] and subplots were the factorial arrangement of Azotobacter chroococcum (inoculated and un-inoculated) and N rate (50, 75, and 100 percent of N recommended rates which were 50, 75 and 100 kg N ha-1, respectively) levels.
Analysis of variance showed that rice paddy yield was significantly affected by crop rotation, Azotobacter chroococcum and N rate. Rice paddy yield in faba bean – rice crop rotation (6174.8 kg ha-1) was significantly lower than fallow – rice (7352.3 kg ha-1) and berseem clover – rice (7554.8 kg ha-1) crop rotations. Moreover, there was no significant difference in paddy yield between fallow – rice and berseem clover – rice crop rotations. Rice paddy yield was significantly increased by 8% after Azotobacter chroococcum inoculation. Rice paddy yield was significantly increased from 6628.8 to 7340 kg ha-1 as N rate increased from 50 to 75 kg ha-1, but further N application (100 kg ha-1) had no significant effect on paddy yield. Of the yield components, panicle number per m2 was significantly affected by crop rotation, Azotobacter chroococcum inoculation and N rate, while grain number per panicle was significantly affected only by crop rotation. Moreover, 1000-grain weight was not significantly affected by any factors. The highest panicle number per m2 was observed in berseem clover – rice crop rotation (352.1 panicles), N fertilizer at the rate of 100 kg ha-1 (362.0 panicles) and Azotobacter chroococcum inoculation (353.2 panicles). The highest grain number per panicle (105.8 grains) was observed in berseem clover – rice crop rotation, while the lowest one (96.3 grains) was observed in faba bean – rice crop rotation.
Based on the result of this experiment, in all crop rotations with rice, the highest paddy yield was obtained in nitrogen application at the rate of 75 kg ha-1 and plants inoculated with Azotobacter chroococcum.