No-tillage effects on grain yield, N use efficiency, and nutrient runoff losses in paddy fields.

The effect of no-tillage (NT) on rice yield and nitrogen (N) behavior often varies considerably from individual studies. A meta-analysis was performed to assess quantitatively the effect of NT on rice yield and N uptake by rice, N use efficiency (NUE, i.e., fertilizer N recovery efficiency), and nutrient runoff losses. We obtained data from 74 rice-field experiments reported during the last three decades (1983-2013). Results showed the NT system brought a reduction of 3.8 % in the rice yield compared with conventional tillage (CT). Soil pH of 6.5-7.5 was favorable for the improvement of rice yield with the NT system, while a significant negative NT effect on rice yield was observed in sandy soils (p < 0.05). N rate, ranging from 120 to 180 kg N ha-1, for at least 3 years was necessary for NT to enable rice yield comparable with that of CT. Furthermore, the observations indicated NT reduced N uptake and NUE of the rice by 5.4 and 16.9 %, while increased the N and P exports via runoff by 15.4 and 40.1 % compared with CT, respectively. Seedling cast transplantation, N rate within the range 120-180 kg N ha-1, and employing NT for longer than 3 years should be encouraged to compromise between productivity and environmental effects of NT implementation in rice fields.