Nitrogen Fertilizer With Different Nitrogen Forms Promoting The Decomposition Of Straw

Multiple cropping index is high about 1.57 in China.The delayed decomposition of straw returning could affect the seedling standing and growth of the following crops.The key to promoting utilization ratio of organic resources and soil fertility was adjusting the C/N of straw in initial stage to realize the efficient straw decomposition.By using the method of net nylon bags,the effect of rice and rapeseed and wheat in different nitrogen forms were studied.Pot experiment was used to study the decomposition,nutrient release and fiber components decomposition of rice straw.Field experiment was used to study the decomposition,nutrient release,soil nutrient and enzymes characteristics of rapeseed and wheat.The major results as follows:1.Pot experiment showed that the decomposition rate of rice straw was fast in the first 30 days,especially in the frist 5 days,and then slowed down until the end of the experiment.In the end of the experiment with 150 days,the cumulative decomposition rate of rice straw was 39.24%-43.70%.In the first 30 days,rice straw was decomposing good under adding PU and UAN.CaCN2 promoted the decomposition of rice straw in the 90th day.In the end of the experiment,the decomposition rate of rice straw were significantly high in adding different nitrogen forms than CK,but it had no difference after adding various nitrogen forms.The sequence of nutrients release of rice straw was K>N>C?P.The release rates of C,N,P and K in rice straw were up to 40.66%-47.31%,44.76%-51.31%,40.46%-46.80%and 94.10%-94.89%,respectively.In the first 10 days,C release rate of rice straw was high under adding UAN and PU.In the first 30 days,N release rate was high under adding UAN and PU.In the first 5 days,P release rate was high under adding UAN.K release fast in the first 30 days,and its release rate was up to 66.20-76.12%,but adding different nitrogen forms had no significant influence to K release.2?In the decomposition process of rice straw,the cumulative decomposition of cellulose and hemi-cellulose results the characteristic of slow decomposition after fast speed,which was consistent with the cumulative decomposition of rice straw.The lignin decomposed slowly at the first 10 days and then fast until the end of the experiment.In the end of the experiment,the cumulative decompositions of cellulose,hemi-cellulose and lignin were 39.10%-43.99%,37.34%-40.08%,and 29.48%-39.50%,respectively.In the first 10 days,addition of UAN and PU significantly promoted the decomposition of cellulose and hemi-cellulose.After 30 days,the fiber components of rice straw decomposed fast in adding CaCN2.3?The field experiment showed that the rapeseed straw decomposed fast in the first 10 days,and the wheat straw decomposed fast in the first 30 days,and then all of them slowed down until the end of the experiment.When the experiment ended in after 120 days,the cumulative decomposition rates of rapeseed and wheat straw were 46.08%-52.34%and 50.94%-53.82%,respectively.In the first 60 days,the cumulative decomposition of rapeseed straw was fast than that of wheat straw.With the increased decomposition of wheat straw,at last,the cumulative decomposition of wheat straw exceeded rapeseed straw.In the fast decomposition period of rapeseed(in the first 10 days),the cumulative decomposition rates after adding UAN and PU was higher than CK significantly.In the end of the experiment,the cumulative decomposition rate of the rapeseed straw was significantly higher than CK in adding different nitrogen forms.For wheat straw,it decomposed fast in the first 30 days,and the result of cumulative decomposition rate was consistent with rapeseed straw except that there were no significant differences among the addition of various nitrogen forms.The sequence of nutrients release of rapeseed was K>P>N>C,while that of wheat straw were K>C>P>N.For rapeseed,in the end of the experiment,release rates of C,N,P,and K were up to 44.25%-51.52%,51.19%-54.87%,52.82%-58.45%,and 96.61%-97.46%,respectively.By contrast,the release rates of wheat straw in C,N,P and K were up to 54.45%-56.34%,47.50%-49.63%,50.49%-55.25%,and 96.44%-97.02%,respectively.C,N and P released rapidly in the first 10 days of rapeseed straw decomposition after adding UAN,and continued to the end of the experiment.The influence of nutrients release of wheat straw was as same as rapeseed straw in different nitrogen forms,but the differences were those nutrients release of wheat straw were fast in the first 30 days,and they had no significant differences among all treatments.The K nutrient released over 95%in the first 5 days.Besides,different nitrogen forms had no obvious effect to the release of K in rapeseed and wheat straw.4?The result of soil enzyme activities showed that,compared with CK,soil urease and cellulose activities increased significantly after adding different nitrogen forms,while catalase had no obvious changes.Sucrase activity improved in rapeseed straw added PU and UAN,while it had no significant difference in wheat straw with addition of different nitrogen forms.