Management Practices For Achieving High Yield And High Resource Use Efficiency Of Rice In Rice-Rice-Rape Cropping System

Improving rice production is extremely important for China’s food security. In order to obtain high grain yield, farmers frequently apply excessive nitrogen fertilizers. Excessive application of nitrogenous fertilizer not only leads to a low nitrogen use efficiency (NUE), but also causes a series of environmental problems. It is, therefore, necessary to explore a good cultivation management to improve both yield and nitrogen use efficiency in rice.Using Rice-Rice-Rape cropping system (2012and2013) and Rice-Rice cropping system (2013) with four N treatments; zero-N application (NO), farmer’s practice (FP), super-high yield (SH), and high yield and high efficiency (HH), a2year field experiment was conducted at two experimental sites (Zhougan and Zhangbang village, Wuxue country). Planting density, N rate and frequence of N application of SH treatement were increased comparing to FP. N rate and planting density of HH treatment were reduced accordingly comparing to SH. Seedling age in Rice-Rice cropping system was shorter than Rice-Rice-Rape cropping system.The present study was carried out with following objectives:(1) to investigate mechanisms of the effects of different treatments on grain yield, nitrogen uptake and use efficiency of early and late season rice;(2) to study mechanisms of the effects of different fields and cropping systems on grain yield, nitrogen uptake and use efficiency of early and late season rice. Data regarding at agronomic traits, grain yield and its components, nitrogen use efficiency and related traits at physiological maturity were recorded. The results obtained are listed as follows:1. Compared with FP, optimized cultivation management can improve grain yield in early season rice of Rice-Rice cropping system and in late season rice of Rice-Rice-Rape cropping system. Grain yield of SH and HH treatment were6.5%and6.3%higher than FP treatment. Yield increasing effect of optimized cutivation management was limited by short growth duration in the main field of Rice-Rice-Rape cropping system in early season rice. A high yield level in late season rice of Rice-Rice cropping system increased the difficulty to yield improvement by optimized cultivation management. Although there are more fertilizers and higher planting density in SH than HH, no yield difference was found between them.2. Compared with FP, optimized cultivation management improved nitrogen uptake and nitrogen recovery efficiency. Nitrogen uptake of SH and HH, were improved by48.7%and57.4%, respectively. Nitrogen recovery efficiency of SH and HH, were improved by18.4%and52.4%, respectively. Nitrogen uptake of HH was20.4%lower than SH, but nitrogen utilization efficiency for grain production, nitrogen utilization efficiency for biomass production, nitrogen physiological use efficiency, agronomy nitrogen use efficiency of HH were23.0%,16.1%,46.9%and43.0%higher than SH, respectively.3. Compared with Rice-Rice-Rape cropping system,6-10days longer growth duration in the main field of Rice-Rice cropping system in early season rice. Furthermore, grain yield of Rice-Rice cropping system was increased by5.1%. Short growth duration in main field maybe an important limiting factor for early season rice. In late season rice, the yield superiority of Rice-Rice cropping system on Rice-Rice-Rape cropping system was lower, shorter seedling age differences between the two systems or longer growth duration may reduced the negative effect of longer seedling age.4. In early and late season rice, grain yield of NO in Zhougan were50.4%and13.2%higher than Zhangbang. Panicles or spikelets per square meter were the main reasons for yield enhancement in early and late season rice. After using nitrogen fertilizer, yield of Zhougan were8.9%and10.6%higher than Zhangbang in early and late season rice. We concluded that fertilizer utilization can reduce the effect of soil potential differences on yield production in the early season rice, nevertheless such effect are not obvious in late season rice.These observations indicated that in Rice-Rice-Rape cropping system, short growth duration in main field restrict grain yield enhancement in early season rice. Optimized cutivation management increased grain yield of late season rice. Compared with SH, HH produced statistically similar yield with less input, and increased nitrogen use efficiency at the same time, so HH is worth to be popularized.