| Rice straw is rich in organic matter, nitrogen (N), phosphorus (P), potassium (K), and it is one of important sources for organic fertilizer in agricultural production. Soil microorganisms can break down straw to release N, P, and K for crop absorbing while decreasing fertilizers inputs and production-devotion ratio, and increasing economic benefits. Heilongjiang is one of the important bases for marketable grain production, and plays a special role in ensuring grain safety in China. In 2014, more than 4 million hectaress of rice were planted in Heilongjiang which caused many straws remained, however, the studies on effects of straw returning on physical-chemical property of soil and plant growth was ignored. A field experiment was carried out to study the effects of whole straw returned on rice growth, yield, accumulation of N, P, K and fertilizer use efficiency under six different N fertilizer levels,0 kg·hm-2,73 kg·hm-2,103kg·hm-2,133 kg·hm-2,163 kg·hm-2, and 193kg·hm-2 in cold region. The study also revealed the regulation of straw decomposition and fertilizer releasing after straw returning and the effects of different amounts of residue (0 kg·hm-2,2500 kg·hm-2, 5000 kg·hm-2,7500 kg·hm-2) incorporation on the contents of paddy soil nutrients were examined. The results were showed as follows:Straw returning decreased the number of tillers during earlier stage. N fertilizer significantly increased rice plant height, tillers, leaf area index (LAI) and SPAD under straw returning, which reached maximum with the fertilizer level 133～193 kg·hm-2. Straw return increased root bleeding, root surface area at tillering period. N increased root bleeding, root length, root surface area, root volume under straw returning, which reached maximum with the fertilizer level 133～193 kg·hm-2. Straw returning was important to increase effective spikes. Under straw returning, with nitrogen application increased, the dry matter accumulation significantly increased which reached maximum in 193 kg·hm-2, and effective spikes, spikelet density increased first and then decreased which reached maximum in 133 kg·hm-2.The accumulation of N, P, K at rice filling stage was inhibited by straw returning. Fertilizer significantly increased the plant N, P, K accumulation. Under straw returning, with nitrogen application increased, N, P and K accumulation of rice plant increased gradually, which reached maximum in 163～193 kg·hm-2. Straw returning also increased nitrogen use efficiency and nitrogen physiological efficiency. Under straw returning, with nitrogen application, nitrogen use efficiency and nitrogen physiological efficiency increased first and then decreased latter.The straw decomposition rates were 51.16% and 26.74% in the first and second year and the two-year accumulative decomposition rate was 78.77%. After two years of decomposing process of rice straw, the contents of C, N, P, K decreased by 12.74%,10.34%,56.25%, 91.04%, respectively. Straw decomposition released C, N, P, and K by 81.47%,80.80%, 81.27%, and 95.41% in two years, respectively.The results indicated that straw application increased contents of soil organic matter, total N, total P, total K, available N, available P, available K, and ammonium nitrogen. With the increase of straw application, the contents of soil organic matter, total P, total K, available N, available P, available K, ammonium nitrogen significantly increased but did not affect the nitrate nitrogen. N fertilizer significantly increase contents of soil total N, available N, NH4+-N but can not affect total P, total K, available P, available K, nitrate nitrogen. The contents of available N and NH4+-N are higher in one month after transplanted and then fall rapidly. N fertilizer significantly increased the content of NH4+-N at the earlier stage, while there was no effect at the latter stage. The content of NO3--N in soil solution was steadily low, which was much lower than that of NH4+-N. N fertilizer had no effect on nitrate nitrogen in soil solution. |
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