Study On The Effects Of Straw Returning To Soil In High-yield Rice-wheat Double Cropping System

The research was carried out in the core zone of national food harvest project in Heheng Farm of Shengao Town, Jiangyan during the years of 2008-2009, and the effects of different seasonal application (single or double cropping) of total straw returning to soil on crop yield, quality, growth and soil fertility were systematically studied through the positionized experimentation of total straw returning of wheat and rice, which provided scientific practical and theoretical basis for field nutrient management, field environment optimization and field ecological improvement, as well as developing a supporting fertilization technique for the mechanical total straw returning under high-yield cropping. The main results are as follows:1. The yield of rice was evaluated by straw reapplication with or without applying fertilizer, and the increase of rice yield was: M2D1> M2D0> M0D1> CG; as for wheat, when applying fertilizer, the yields of M1D1, M1D0 and M0D1 were higher than CG by 42.49kg/667m2, 30.04kg/667m2 and 26.86kg/667m2, with the increased degree of 9.35%, 6.61% and 5.91%, respectively. In all sorts of tests, the differences between those with straw returning and those without it were all significant; the reapplication of rice-wheat double cropping straw attained the best effect on the yield of wheat, better than the reapplication of single straw returning; among the latter treats, effect of wheat straw incorporation slightly surpassed that of rice straw; the increased yield was enhanced with raising cropping seasons of straw returning. Increased production of rice was mainly due to the more profitable grains per panicle, 1000-grain weight, and seed setting rate, and grains per panicle and 1000-grain weight for wheat. Straw returning would increase considerable yield increase in the case of certain spikes per 667m2 for rice and wheat.2. Rice straw returning led to increased polished rice rate, reduced size of chalkiness, lower grain length and larger width and thickness of grains. Furthermore, the returning to soil of straw showed a tendency of increasing the gel consistency and the percentage of amylase, raising the peak viscosity, trough viscosity, final viscosity and the duration of peat viscosity, and cutting down the viscosity setback. All the changed results mentioned above showed positive correlation to the season times of straw returning as well as better effects of current seasonal reapplication than the reapplication during the other season.With or without fertilization, incorporation of straw promoted the intake of trace elements (Cu, Fe, Mn, Zn) into rice flour, with the treat that M2D1 was the most favorable to the improvement of various trace elements. Possibly due to the durative nitrogen supplying capability in late growth periods with straw returned to soil, the grain protein content of wheat was especially increased, and the sedimentation value and bulk density of wheat grains were also improved.3. Wheat straw returning showed a short-term inhibition activity on rice tillering at initial tillering stage, which would reduce as the cropping seasons of straw reapplication increases. In late tillering stage, straw incorporation enhanced the ability of tiller sustaining of rice plants, ensuring sufficient yield spike at maturity to achieve high yield. Returning of current season rice straw affected the emergence of wheat seedlings, slightly reduced the basic seedling number, while in late tillering stage it showed great promoting effect on the tillering process and in the end ensured enough wheat spikes at maturity. Returned straw would help rice and wheat attain larger and suitable LAIs in heading and maturity stages, providing adequate source for later grain filling and getting a more coordinated relationship between source and sink. The positive effects total straw returning to soil were displayed rather obviously after the jointing stage, increasing grains per panicle and 1000-grain weight of rice and wheat and significantly enhancing dry matter accumulation during the period from heading to maturity. Among all the treats, the total reapplication of straw of rice and wheat in double cropping seasons was more than the most favorable to performance the preceding features.4. Under the condition of fertilization, straw returning would increase soil organic matter content and the increment range was in positive correlation with the number of cropping seasons reapplying straw. Soil organic matter would show a downward trend in the absence of straw returning. As for the soil alkali-hydrolysable nitrogen, a significant aspect of soil ability of nitrogen immediate support, it was relatively less influenced by the straw returning, but with an evident tendency of soil available nitrogen. Straw returning under chemical fertilizer could increase available potassium and phosphorus content in soil, and with increased times of cropping seasons of straw incorporation, the effect was more obviously observed. Therefore, straw returning could help improve soil available phosphorus and potassium. Straw returning to soil also enhanced the ability of rice and wheat to absorb soil nitrogen, phosphorus and potassium, raised accumulated N, P and K uptake of rice and wheat plants, increased the seasonal fertilizer utilization efficiency, and promoted their yield on the basis of higher plant growth. rice and wheat straw seasons best and most conducive to the performance of these characteristics. The total reapplication of straw of rice and wheat in double cropping seasons was the most favorable to performance the preceding features.In summary, under existing cropping system and fertilization level, total straw returning to soil could increase yield, improve grain quality, improve soil ability for fertilizer supplying and retaining, as well as enhance the seasonal nitrogen utilization efficiency, which was beneficial to the coordination and harmonization of high-yield, high efficiency, high quality, ecology, and security.