Effects of straw returning plus fertilization on soil organic carbon components and crop yields in rice-rapeseed rotation system

ObjectivesRice-rapeseed rotation is one of the main rotation systems in China, in which large amounts of fertilizer are applied. Straw return is the most direct way to use straw in China. Therefore, studying the proper way of combined use of straw and chemical fertilizer will be beneficial to increase rice and rape yields, improve soil fertility, and promote application of the straw return technology with fertilizers in the lower Yangtze region.

MethodsA field experiment was conducted consecutively for seven-years and 13 seasons in Anhui Province. Five treatments were designed including no nitrogen fertilizer no straw returning (CK), only chemical fertilizer application without straw returning as farmer's practice pattern (FPP) and three levels of fertilizer application plus rice straw return of 3000 kg/hm²(SF1, SF2 and SF3). The contents of soil total organic carbon (TOC) and its components, the crop yields and net benefits in rice-rapeseed rotation fields were investigated.

ResultsCompared with the FPP, treatments of SF1, SF2 and SF3 increased the contents of TOC, humilic acid carbon and humin carbon by 5.6%-12.1%, 9.0%-22.6% and 7.9%-10.2%, respectively, increased the contents of total nitrogen, available phosphorus and available potassium by 6.7%-14.0%, 134.7%-249.5% and 40.2%-70.5%, not increase the contents of water-soluble organic carbon and fulvic acid carbon. The average yields of rice and rapeseed and the total yields of the two seasons were increased by 8.6%-19.3%, 19.1%-27.3% and 10.3%-24.1%, and the net profit and cost were increased by 1651-4905 and 1427-2882 yuan/hm². The highest contents of soil organic carbon components, nutrients and crop yields were observed in the SF3, however, there was no significant difference in the yields of rice and rapeseed between SF3 and SF2 with reducing the amount of fertilizer 255 kg/hm². The relationships among the soil organic carbon components, nutrient contents and crop yields were significant or extremely significant. The stepwise regression analysis showed that soil total N, humic acid and water soluble organic carbon content were the key factors determining the yields of rice and rapeseed.

ConclusionNPK fertilizers plus straw returning are effective to increase soil total carbon accumulation and soil fertility, improve the crop yields. In spite of higher inputs in labor and fertilizers, the straw returning plus proper fertilizer application rate is still profitable in rice and rapeseed rotation system.