Effects Of Nitrogen Fertilization And Rice Straw Returning Methods On Soil Biological Activities And Grain Yield In Wheat

The rice straw returning is an important way of resource utilization, and it is of vital importance to increase the content of soil organic matter and improve the physical and chemical properties of soil. However, the unreasonable returning methods and inappropriate application methods of nitrogen fertilizer not only leads to the decline in grain yield, increase the cost of production, but also caused pollution and soil environment destruction. To make clear the effects of yield and soil biological activity in wheat and its physiological basis under nitrogen fertilizer and returning methods can provide the theoretical basis and decision support for high yield cultivation of wheat. Therefore, the influence of rice straw under nitrogen fertilizer and mulching on wheat growth, yield, soil physical and chemical properties and biological activity of soil are studied by field experiment. The main results were as follows:1. Effects of nitrogen basal to topdressing ratios and returning methods on wheat yield and nitrogen use efficiency of influence. The results showed that the rice straw returning reduced the emergence of wheat, ear number, but it significantly increased the grain number per spike,1000 grain weight resulting in the increase in wheat yield. It also increased the SPAD content after anthesis, dry matter accumulation, and stage of nitrogen utilization of wheat. The maximum wheat yield was observed at ratio of basel to topdressing being 7:3 under nitrogen fertilizer and at from rotary tillage among the returning methods. It indicated the we should use the from rotary tillage and the basel to topdressing being 7:3 which can effectively improve the wheat yield and nitrogen use efficiency under rice straw returning full.2. Effects of nitrogen basal to topdressing ratios and returning methods on the physicochemical properties of soil under the rice straw returning. The results showed that rice straw returning reduced soil water content, soil bulk density and pH value but increased soil temperature. The mulching treatment among returning methods increased the soil water content and soil bulk density. In addition, our studies also showed that the application of nitrogen fertilizer could significantly increase the ammonium nitrogen content and nitrate nitrogen content in the 0-40cm soil layers. Furthermore, inorganic nitrogen content increased with the increase in application of base fertilizer before the pre-jointing fertilizer, rice straw returning reduced the content of soil inorganic nitrogen from sowing to overwintering, but increased it from overwintering to anthesis. And the maximum inorganic nitrogen was observed at ratio of basel to topdressing being 7:3 under nitrogen fertilizer and at from rotary tillage among the returning methods after wintering period. Which being order to improve the yield and nitrogen use efficiency.3. Effects of ratio of nitrogen basal to topdressing and returning methods on the quantity of soil microorganism under rice straw returning. The results showed that, the quantity of soil microorganism increased significantly by increasing the amount of basal fertilizer in the experiment of ratio of nitrogen basal to topdressing. The quantity of bacteria, fungi and actinomycetes increased by 22%,25%,49% compared with straw removed, respectively. What’s more, in the 0-20cm soil layers, the numbers of bacteria had the highest increase at rotary tillage, while the numbers of fungi and actinomycetes had the highest increase at deep plowing among the returning methods. However, in the 20-40cm soil layers, the numbers of bacteria had the highest increase at rotary tillage, while the numbers of fungi and actinomycetes had the highest increase at deep plowing among the returning methods.4. Effects of nitrogen basal to topdressing ratios and returning methods on the activity of soil enzyme under rice straw returning. The research showed that, the content of soil catalas, urease, neutral phosphatase increased by increasing the amount of basal fertilizer in the experiment of ratio of nitrogen basal to topdressing. In addition, invertase content increased under suitable basal to topdressing ratio and the maximum was observed at 6:4. Straw returning significantly increased the activity of soil catalase, invertase, urease and neutral phosphatase. Furthermore, in the 0-20cm soil layers, neutral phosphatase had the greatest increase under from rotary tillage; soilcatalase and invertase had the greatest increase under rotary tillage; urease had the greatest increase under deep plowing treatment. However, in the 20-40cm soil layers, neutral phosphatase had the greatest increase under from rotary tillage; urease had the greatest increase under rotary tillage;invertase had the greatest increase under deep plowing.In conclusion, under returning of rice straw, the ratio of nitrogen basal to topdressing at 7:3 can increase the yield of wheat and improve soil biological activity. Because the treatment provided sufficient nitrogen for soil microorganism by increasing basal fertilizer to increase the activity of soil enzyme. As a result, the ammonium nitrogen content and nitrate nitrogen content in soil increased, which was helpful to nitrogen fixation at the early stage and release at the later stage, regulating the soil N supply for wheat to increase the absorption and utilization efficiency of nitrogen in wheat. Among the returning methods, the from rotary tillage is returning for relatively high rate of emergence, and the number of soil microorganism and soil enzyme activity increase more than some returning methods, so it improved the soil physical properties and soil nitrogen supplying capacity to increase the grain yield of wheat.