Response Mechanism Of Nitrogen Transformation In Chernozem On Straw Returning With Nitrogen

Chernozem is one of the main types of soils in agricultural production in Jilin Province.Long-term tillage leads to the decrease of organic matter content and the depletion of soil nitrogen gradually.Therefore,it is vital to increase the organic matter content of chernozem,which is beneficial to the sustainable development of agriculture.Therefore,the typical chernozem in Jilin Province was selected as the research object to study the effects of different straw addition（without adding straw,half amount of straw,total amount of straw,2 times of straw and 5 times of straw.）and the combined application of urea and diammonium hydrogen phosphate(the application of urea and diammonium phosphate were 557.46 kg·hm^-2 and 1225.84 kg·hm^-2,respectively.)on organic carbon（SOC）accumulation and nitrogen transformation of chernozem through laboratory simulation culture.The main results are as follows:（1）The contents of organic carbon and total nitrogen（TN）in chernozem were increased with the increase of straw addition,and the addition of straw increased the SOC content of chernozem by 6.27%-31.84%,and the addition of straw increased the TN content of chernozem by 3.31%-14.05%,respectively.The combined application of urea and diammonium hydrogen phosphate significantly increased the content of SOC and TN in chernozem,and the improving effect of diammonium hydrogen phosphate was better.Straw addition increased the C/N ratio of chernozem,and the C/N ratio was increased greatly with the increase of straw addition,and the addition of straw increased the C/N ratio of chernozem by 3.24%-16.01%.The addition of urea and diammonium hydrogen phosphate significantly reduced the C/N ratio of chernozem,and the treatment with diammonium hydrogen phosphate was decreased greatly.（2）The contents of microbial biomass carbon（SMBC）and microbial biomass nitrogen（SMBN）in chernozem were increased after straw returning,and the contents were increased greatly with the increase of straw addition.The addition of straw increased the SMBC content of chernozem by 64.66%-196.46%,and the addition of straw increased the SMBN content of chernozem by 102.58%-195.84%.The combined application of nitrogen significantly increased the content of SMBC and SMBN in chernozem,and the promoting effect of diammonium hydrogen phosphate was better than that of urea.According to the SMBC/SMBN ratio,it was concluded that the microbial community in chernozem was dominated by fungi.The combined application of nitrogen decreased the SMBC/SMBN ratio of chernozem.（3）The results of interaction analysis showed that the interaction of two times amount of straw and urea（or diammonium hydrogen phosphate）had more obvious effect on the promotion of SMBC in chernozem.The interaction of five times amount of straw and urea had more obvious impact on the promotion of SMBN,and the interaction of two times amount of straw and diammonium hydrogen phosphate had more significant impact on the promotion of SMBN of chernozem.The results showed that high amount of straw returning combined with nitrogen was more beneficial to the growth of microbial biomass in chernozem.（4）After straw returning to field,the contents of mineral nitrogen and net nitrogen mineralization of chernozem decreased,and the contents were decreased rapidly with the increase of straw addition.With the addition of straw,the mineral nitrogen content of chernozem was reduced by 35.38%-98.07%,and the net nitrogen mineralization was reduced by 52.70%-103.32%.The combined application of nitrogen significantly increased the content of mineral nitrogen and net nitrogen mineralization in chernozem,and the improving effect of urea was better than that of diammonium hydrogen phosphate.（5）Straw returning decreased the average net nitrification rate of chernozem,and the average net nitrification rate was decreased greatly with the increase of straw addition.The addition of straw decreased the average net nitrification rate of chernozem by 32.35%-97.06%.The combined application of nitrogen significantly increased the average net nitrification rate of chernozem,and the improving effect of urea was better than that of diammonium hydrogen phosphate.