Effects Of Straw Full Incorporation On Rice Growth And Soil Fertility

In order to explore the effect of full rate of straw returning on rice growth and soil fertility, a field experiment was carried out in2010and2011to dertermine the effect of straw returning and ash returning after straw burning on double rice growth and development, yield and quality as well as soil nutrient supply, utilization and biological properties. The objective of this study is to elucidate the effect of straw returning under the equal amount of nutrient application on soil fertility, rice growth, and their relationships.The main results are as follows:1. Effects of straw returning on rice growthAfter2-year straw returning, both early and late rice yields were higher in the straw returning treatment (NPK+S) than in no-straw returning ones (NPK+SI), and were slightly lower than in the ash returning ones. Under no inorganic fertilization, grain yields were significantly higher in the straw returning treatment than in the ash returning and no-fertilizer control. Straw returning increased the number of effective panicles compared with the NPK+SI and NPK treatments in early rice, while reducing that relative to the NPK treatment in late rice. The percentage of grain filling was highest under straw returning, but it was no significantly differences with the percentage of grain filling,the number of spikelets and the1000-grain weight in every treatment.Under no inorganic fertilization, straw returning led to the greatest number of effective panicles and grains per panicle.Straw returning increased the tillering rate, spike rate in early rice, but was not beneficial for the growth of tillers in late rice. Straw returning improved the leaf area index in the med-and late-stage of early rice, which was lowest throughout the whole growth period and was significantly higher in CK+S than other treatment under no inorganic fertilization. The2-year experiment showed that the dry matter biomass was higher in NPK+S than NPK+SI and NPK in both early and late rice. Straw returning increased the output rate, conversion rate and contribution rate of stem and leaf in early rice, but had no marked effects in late rice.Under equal nutrient application, straw returning increased the content of non structural carbohydrate, assimilation and transport efficiency and C/N of stems at heading stage and mature stage, while no significant trends were found in late rice.SPAD values in flag leaf after heading was higher in NPK+S and in NPK+SI and NPK in early rice, while showing the opposite trend in late rice. Root activity was lower in NPK+S than in NPK+SI and NPK in early rice with no significant differences in late rice. The spikelet-bleeding-intensity was higher in NPK+S than in NPK+SI and NPK at heading stage, whereas no significant trends were observed in late rice. The total absorption of nitrogen, phosphorus, and potassium was higher in NPK+S than in NPK+SI and NPK in both early and late rice. The nitrogen use efficiency did not differ among various treatments. The needed amount of K2O per100-kg grains was higher in NPK+SI than in NPK+S and NPK, while that of N and P2O5showed no differences. The total uptake of N, P, and K was closely correlated with yields in both early and late rice.Straw returning improved the processing and eating quality of rice grains, but reduced the appearance and nutrition quality. Straw returning reduced the fertilizer cost, and increased the economic profits that were higher in early than late rice.2. Effects of straw returning on soil fertilityStraw returning after2years reduced soil bulk density, increased soil total porosity, aeration porosity and holding soil moisture, and were beneficial for soil physical properties, but ash returning tended to reduce soil physical properties.The content of soil nitrogen, phosphorus, and potassium showed no consistent trends under different straw returning regimes. Overall, straw returning increased the content of alkali-hydrolyzable nitrogen, available nitrogen and slow release potassium, while had no significant effects on total nitrogen, available phosphorus, available potassium and available potassium.The results showed that4-season straw returning improved the content of total soil organic carbon, active organic carbon, mineralizable carbon and its efficiency, especially labile organic carbon and carbon mineralization. The soil steady carbon had no significant differences among various treatments. The carbon pool management index was significantly greater in NPK+S than NPK+SI and NPK. Correlation analyses showed that the soil carbon pool management index showed significant parabola relationships with both early and late rice yields, and the correlation coefficient was0.9999**and0.9798*for early and late rice, respectively.Straw returning increased the total biomass of three microbial categories in early rice, but reduces that in late rice. The microbial biomass was in the order:bacterial> actinomyces> fungi, irrespective of straw returning regimes.The activity of sucrose enzyme was greater in NPK+S than in NPK+SI and NPK, while the urease activity was significantly lower than the latter two with no significant differences in the catalase activity. Invertase, urease and catalase were significant correlated with soil organic matter, nitrogen, potassium, soil carbon forms and efficiency as well as carbon pool management index.Straw returning increased soil methane emissions, as nitrous oxide, rice straw is lower than the straw is not the field, but higher than the straw burning ash to field straw burning ash field has increased the produce of the soil carbon dioxide.