Effects Of Carbon And Nitrogen Fertilizer Addition On Crop Residue Decomposition And Soil Nitrogen Transformation

The effects of exogenous nitrogen?N?and carbon?C?additions on crop residue decomposition were controversial,and the nutrient release pattern was unclear.In this study,a laboratory incubation experiments and a field experiment were established to investigate crop residue decomposition and soil nitrogen transformation.The incubation experiment include two soils?Lime concretion black soil :LS and Alluvial soil :AS?,two C levels?C0 and C1:200ppm?and three N levels?N0,N1:180kg N ha-1;and N₂ :360kg N ha-1?for wheat and corn residue decomposition.The field experiment include three N fertilizer treatments?CK,N180:180kg N ha-1,N360:360kg N ha-1?,and the residue was placed on the surface?0 cm?and buried at a depth of 20 cm?20 cm?.The decomposition rate,soluble sugar,organic carbon,nitrogen,phosphorus content,soil NO₃^--N,NH4+-N content,N₂ O emission flux were measured.Correlation analysis was used to analyze the relationship between residue and soil properties and decomposition rate.The results showed that under laboratory conditions,corn straw decomposition rate is higher than that of wheat straw,at the end of the incubation,in LS and AS,the average values are higher than 17.05% and 6.73%;wheat straw in AS decaying faster than LS 9.92%,maize straw in the two kinds of soil decomposition rate is basically the same.The addition of glucose,the decomposition constant of wheat straw increased significantly.Nitrogen fertilizer could promote wheat straw decomposition,and with the increase of nitrogen,decomposition rate increased.There are significant differences among different nitrogen application rates.The carbon and nitrogen on corn straw decomposition are not affected.In the field experiment,nitrogen fertilizer had no effect on the decomposition of surface straw,but promoted the decomposition of wheat straw and inhibited the decomposition of corn straw at a depth of 20 cm.In the two kinds of soil,the soluble sugar content of straw decreased rapidly in the first 30 d,then kept at a low level.At the end of incubation,the organic carbon content of wheat and corn straw decreased by 1.64% and13.26%.Under field conditions,the organic carbon content of wheat straw increased by 14.81%,while that of corn straw decreased by about 2.21%.In lab incubation and field,the averagenitrogen content of wheat straw increased by 81.39% and 53.04%,respectively,and the phosphorus content decreased by 69.05% and 74.09%,respectively;the nitrogen content of corn straw increased by 14.45% and 1.92%,respectively,and the phosphorus content decreased by 20.47% and 29.67%,respectively.In the field,the amount of nutrient release of underground straw was significantly higher than that of aboveground straw.In LS and AS,the addition of carbon and nitrogen could promote the release of soluble sugar,organic carbon,nitrogen and phosphorus from wheat straw,but had no effect on the nutrients release from corn straw.In the field,nitrogen addition could promote the release of nutrients in wheat straw,but inhibited the release of nutrients in corn straw.In lab incubation,the content of NO₃^--N in wheat straw increased gradually.The content of NO₃^--N in soil was decreased by adding straw.With the addition of carbon,the NO₃^--N content of wheat straw was increased under the condition of high nitrogen content in AS,and increased under the condition of middle nitrogen content in LS.The nitrogen content increased significantly under the condition of nitrogen in the soil.Nitrogen addition significantly increased the soil NO₃^--N content..The soil NH4+-N content decreased gradually during the incubation period,and the addition of carbon and nitrogen had no effect on the soil NH4+-N content.The addition of straw,carbon and nitrogen mainly changed the soil inorganic nitrogen status by changing the NO₃^--N content.The nitrification rate of corn straw was significantly higher than that of wheat straw,which was 101.79% and 135.34% higher than that of wheat straw in AS and LS.Carbon had no effect on nitrification rate and ammonification rate.Nitrogen could significantly change the nitrification rate of straw,and increased with the increase of nitrogen application rate,compared with CK,N0,N1,and N₂ were increased by-14.96%,52.74%,respectively.The accumulation of NH4+-N was significantly lower than that of NO₃^--N.The addition of carbon had no effect on the accumulation of inorganic nitrogen,and nitrogen significantly increased the accumulation of soil nitrogen.The emission flux of N₂ O showed a dynamic change and remained at a low level after 30 d.The N₂ O emission flux in AS was significantly higher than that of LS.After adding straw,the N₂ O emission flux increased.Addition of carbon had no significant effect on the mean flux of N₂ O emissions,and the addition of nitrogen significantly increased the emission flux of N₂ O.The results of correlation analysis showed that the decomposition rate of wheat straw was positively correlated with the content ofnitrogen,phosphorus,NO₃^--N,NH4+-N content in lab incubation;The decomposition rate of maize straw was only positively correlated with the content of soluble sugar,phosphorus and NH4+-N.In the field,wheat and corn straw decomposition rate was significantly correlated with the organic carbon,nitrogen,phosphorus content,C/N,N/P,NO₃^--N,NH4+-N content,corn straw decomposition rate also had significant correlation with C/P.