[Effects of increased planting density with reduced nitrogen fertilizer application on rice yield, N use efficiency and greenhouse gas emission in Northeast China].

The traditional rice growing practice has to change to save resource and protect environment, and it' s necessary to develop new technology in rice cultivation. Therefore, a two-year field experiment of Japonica rice (Liaoxing 1) was conducted in Northeast China in 2012 and 2013 to investigate the integrated effects of dense planting with less basal nitrogen (N) and unchanged top-dressing N (IR) on rice yield, N use efficiency (NUE) and greenhouse gas emissions. Compared with traditional practice (CK), we increased the rice seedling density by 33.3% and reduced the basal N rate by 20%. The results showed that the average N agronomy efficiency and partial factor productivity were improved by 49.6% (P<0.05) and 20.4% (P<0.05), respectively, while the area and yield-scaled greenhouse gas emissions were reduced by 9.9% and 12.7% (P<0.05), respectively. Although IR cropping mode decreased panicle number and biomass production, it significantly enhanced rice seed setting rate and harvest index, resulting in an unchanged or even highei yield. NH4+-N and NO3(-)-N concentrations in rice rhizosphere soil were reduced, resulting in an increment of N recovery efficiency. Generally, proper dense planting with less basal N applicatior could be a good approach for the trade-off between rice yield, NUE and greenhouse gas emission.