Research About Characteristics Of Nitrogen Transformation And Acidity Change Of Chernozem Driven By Exogenous Nitrogen

Chernozem is the main type of soil for corn production in Jilin Province.However,in recent years,irrational fertilization has led to the acidification trend of chernozem,the addition of exogenous nitrogen and soil acidification would affect the change of soil acidity and nitrogen conversion.Therefore,this research selected chernozems with different acidity in Jilin Province（p H values are 5.38,6.54,7.16 and 8.11,No.A,B,C and D）as the research object,The effects of urea and diammonium phosphate on NH₄⁺-N content,NO₃^--N content,SMBC content,SMBN content,soil acidity and acid-base buffering property of chernozem were studied by simulated culture experiment.The aim of this research was to elucidate the nitrogen transformation mechanism and soil acidity change characteristics of chernozem with different acidity after the addition of exogenous nitrogen.Furthermore,theoretical basis for rational fertilizer application,ecological environmental protection and sustainable agricultural development in chernozem region of Jilin Province was provided.The results are as follows:（1）After the application of urea and diammonium phosphate,the contents of NH₄⁺-N,NO₃^--N,SMBC,SMBN,nitrification and mineralization of chernozem with different acidity levels were significantly increased.In comparison,the addition of urea was beneficial to the increase of NO₃^--N content,nitrification and mineralization rate of chernozem.The addition of diammonium phosphate was beneficial to the increase of NH₄⁺-N content and SMBC content and SMBN content of chernozem.（2）After the application of urea and diammonium phosphate,the content of NH₄⁺-N and NO₃^--N in chernozem with different acidity were in the order of A>B≥C>D and D>A>C≥B,the nitrification rate and mineralization rate were in the order of D>C>A>B and D>A>C>B,the content of SMBC and SMBN were in the order of D>C≥B>A and D>C>B>A.The content of SMBC and SMBN were decreased and the content of NH₄⁺-N was increased with the decrease of the p H value of chernozem.The NO₃^--N content of acidic and alkaline chernozem was higher than that of neutral chernozem.The chernozem with the neutral p H had the less nitrification and mineralization rate.（3）Urea and diammonium phosphate reduced the p H of the four chernozems by 0.44,0.51,0.61,0.36 and 0.52,0.55,0.86 and 0.42 units,respectively.For the four soils,the degree of p H reduction was in the order of C>B≥A>D.（4）After the application of urea and diammonium phosphate,the p H of soil sample D is still alkaline,so the exchangeable acid,H⁺and Al³⁺are not detected.The content of exchangeable acid,H⁺and Al³⁺in soil samples A,B and C were all increased to varying degrees.The content of exchangeable acid,H⁺and Al³⁺was in the order of A>B>C.For the treatment of diammonium phosphate,the content of exchangeable acid,H⁺and Al³⁺in chernozem with urea was not significantly different.The p H value of chernozem was in the range of neutral acidity,and the content of exchangeable acid,H⁺and Al³⁺was increased with the decrease of soil p H value.（5）After the addition of urea and diammonium phosphate,the acid-base buffer capacity of the four soil samples were decreased by 2.82,10.27,3.24,2.99%and 2.26,3.80,3.70,3.94%,respectively.There is no significant difference between the effects of the two fertilizers.The acid-base buffer capacity of chernozem was significantly positively correlated with soil p H and cation exchange capacity,and is positively correlated with organic matter content.In conclusion,urea and diammonium phosphate could improve the content of NH₄⁺-N,NO₃^--N,SMBC and SMBN,nitrification and mineralization rate of chernozem.The content of exchangeable acid,H⁺,Al³⁺in chernozem with different acidity could also be increased.the soil p H and acid-base buffering capacity were reduced.the whole effect led to increasing chernozem acidification.