Abstract: Rice-rapeseed rotation is one of the most important agricultural cultivation systems in China. Intensive farming in such systems would reduce soil fertility. Straw returning is one of the main ways to use straw in China. A field experiment was conducted to examine effects of straw returning plus fertilization on crop yield, nutrient accumulation, fertilizer use efficiency and nutrient balance in rice-rapeseed rotation. There were five treatments, including no nitrogen fertilizer and straw returning (CK), chemical fertilizer application without straw returning as farmer’s practice pattern (FPP) and three practices of fertilizer application mixed with rice straw returning of 3000 kg·hm^-2 (FS1, FS2 and FS3), in which nitrogen, phosphorus, and potassium fertilization levels were gradually increased from treatment FS1 to FS3. The results showed that yields of rice and rapeseed had similar patterns under different treatments of straw incorporation and fertilizer application, being SF3>SF2>SF1>FPP. However, there were no significant differences in rice and rapeseed yield between treatments SF2 and SF3. Compared with FPP, annual yield increased on average by 17.5%-28.6% under treatments of straw returning with increased fertilization levels, and the amount of nitrogen, phosphorus and potassium accumulated in rice and rapeseed increased with increasing fertilization level. Nitrogen, phosphorus and potassium accumulations in rice increased on average by 21.7%, 17.7% and 14.0%, and those in rapeseed increased by 22.4%, 19.6% and 51.8%, respectively. The enhancement of potassium accumulation in rapeseed was the highest due to returning straw and applying more potassium fertilizer. Under treatments of straw returning plus fertilization, nitrogen partial factor productivity (PFP_N) increased by 8.1% to 31.1% for rice and 4.2% to 29.3% for rapeseed respectively, compared with the treatment of FPP, similar to the results of nitrogen agronomic efficiency (NAE). SF2 had higher PFP_N and NAE, but lower phosphorus and potassium partial factor productivity.Results of nutrient balance calculation showed that phosphorus and potassium was deficient in rice, and was surplus and beyond the acceptable range in rapeseed under treatments of strawreturning with fertilizer applications. In the ricerapeseed rotation system, straw returning plus fertilizerapplication could improve crop yield, nutrient accumulation, and fertilizer use efficiency. However, the large amount of phosphorus and potassium fertilizer input and the nutrients from straw returning caused surplus of nutrients and decrease of fertilizer use efficiency. Therefore, it is necessary to further adjust the input amount of chemical fertilizer under straw returning to make more reasonable and sustainable nutrient recycle and use in crop production system.

Key words: Korean pine broad-leaved forest, fire resistance, bark, entropy weight method.