| The Loess Plateau is one of the most important grain producing areas in China,and nitrogen application is one of the most important measures to ensure the grain yield.In order to pursue higher crop yields,the phenomenon of excessive nitrogen application is widespread in this area.However,excessive nitrogen application will not only increase production capital but also cause a series of environmental problems,such as eutrophication of water bodies,greenhouse gas emissions and soil acidification.Therefore,reducing nitrogen loss and improving nitrogen utilization efficiency are the urgent problems to be solved in the current sustainable development of agriculture.In this study,a three-year field experiment was performed in Changwu,Shaanxi Province,to investigate(1)the response of soil(0-40 cm)nitrification and denitrification microorganism quantity and activity to nitrogen reduction and straw returned to the field;(2)the effect of nitrogen reduction,straw returned to the field,mixed controlled-release fertilizer and added nitrification inhibitor on spring maize yields and the residual amount of nitrate nitrogen in the soil,so as to provide a theoretical basis for improving the nitrogen management models of maize field in the Loess Plateau area.The experiment was performed from april 2017 to september 2019 in the rain-fed agricultural area of the Loess Plateau.The experiment included 12 treatments,including CK(no nitrogen application),N200(nitrogen reduction mode,200 kgN/hm~2),N200+S(nitrogen reduction mode+straw returned to the field,200 kgN/hm~2),N250(conventional nitrogen fertilization mode,250 kgN/hm~2),N250+S(conventional nitrogen fertilization mode+straw returned to the field,250 kgN/hm~2),NC0(100%urea+0%controlled-release urea,200 kgN/hm~2),NC65(35%urea+65%controlled-release urea,200 kgN/hm~2),NC50(50%urea+50%controlled-release urea,200kgN/hm~2),NC35(65%urea+35%controlled-release urea,200 kgN/hm~2),DCD0(without nitrification inhibitor dicyandiamide,200 kgN/hm~2);DCD1(the addition concentration of nitrification inhibitor is 1%of nitrogen application amount,200 kgN/hm~2),DCD5(the addition concentration of nitrification inhibitor is 5%of nitrogen application amount,200 kgN/hm~2).The yield of spring maize and nitrate nitrogen content in soil profile(0-300 cm)at harvest period,the soil microbial biomass carbon and nitrogen,and the soil nitrification potential on the third day after fertilization and at the spring maize silking stage were measured.Under nitrogen reduction and straw returned to the field,the physical and chemical properties on the third day after fertilization and the copy number of nitrification and denitrification microbial functional genes of the 0-40cm soil layers on the third day after fertilization and at the spring maize silking stage were measured.The main results are as follows:1.Under nitrogen reduction and straw returned to the field,the number of ammonia-oxidizing archaea(AOA)is higher than ammonia oxidizing bacteria(AOB),but compared to AOA,AOB is more affected by nitrogen and straw returned to the field.When the nitrogen rate is 200 kgN/hm~2,straw returned to the field can significantly increase the gene copy number of AOB-amoA in soil.Under the same nitrogen rate,straw returned to the field significantly increase the gene copy number of denitrifying microorganisms such as nirK(0-40 cm),nosZ(0-20 cm)and narG(0-20 cm),has little effected on nirS gene.In addition,the gene copy number of nitrifying and denitrifying microorganisms in soil is significantly affected by soil depth.2.To some extent nitrogen reduction with straw returned to the field,nitrogen reduction with mixing different ratios controlled-release fertilizer and nitrogen reduction with adding different concentrations of nitrification inhibitor will increase soil microbial biomass carbon and nitrogen.Under the same nitrogen rate,compared with N200,the N200+S significantly increased the microbial biomass carbon and nitrogen content in 0-40cm soil layer by 14.1%-19.9%and 30.8%-49.6%,respectively.Compared with N250,the N250+S increased the microbial biomass carbon and nitrogen content in 0-40cm soil layer by 12.7%-17.5%and 23.9%-45.9%respectively.Compared with total urea treatment(NC0),the treatments of nitrogen reduction with mixing different ratios controlled-release fertilizer increased the microbial biomass carbon content in 0-40cm soil layer by 7%-9.8%(NC35),11.9%-17.4%(NC50),9.1%-14.0%(NC65),respectively;compared with NC0,the microbial biomass nitrogen content increased by 2.8%-8.0%(NC35),23.2%-41.6%(NC50)and 15.1%-24.8%(NC65),respectively.Compared with DCD0,the treatments of nitrogen reduction with adding different concentrations of nitrification inhibitor increased the microbial biomass carbon content in 0-40cm soil layer by10.2%-16.8%(DCD1)and 7.0%-10.6%(DCD5)respectively,and the microbial biomass nitrogen content increased by 21.2%-32.8%(DCD1)and 5.6%-12.1%(DCD5),respectively.3.Compared with CK,the nitrification potential of soil increased significantly in each nitrogen fertilization treatment,and gradually increased with the increase of nitrogen fertilization,while nitrogen reduction with straw returned to the field,nitrogen reduction with mixing different ratios controlled-release fertilizer and nitrogen reduction with adding different concentration of nitrification inhibitor decreased the nitrification potential of soil in varying degrees.In this study,compared with N250,the nitrification potential of N200 reduced by 4.5%-14.3%;compared with straw not returned to the field,the nitrification potential of straw returned to the field decreased by 15.4%-28.6%;compared with NC0,the nitrification potential of NC50 decreased by 16.7%-42.9%;compared with DCD0,the nitrification potential of DCD1 decreased by 11.5%-28.6%.4.Reduced nitrogen by 20%on the basis of traditional nitrogen application was not reduced the yield of spring maize.The average spring maize yield of 3 years of N200 treatment is 6.1%higher than traditional N250(p<0.05);under the same nitrogen rate,the yield of spring maize in straw returned to field is higher than that in straw not returned to field,compared with N200,N200+S increased the yield of spring maize by 7.2%(p<0.05);compared with N250,N250+S increased the yield of spring maize by 9.2%(p<0.05).The average spring maize yield of 3 years of NC65 and NC35was lower than NC0,reduced by 5.8%and 14.4%,respectively.There was no significant difference between NC50 and NC0(p>0.05).The spring maize yield was decreased by adding different concentrations of nitrification inhibitor,compared with DCD0,the average spring maize yield of 3 years of DCD1 and DCD5 was reduced by 6.5%(p<0.05)and 4.3%(p>0.05),respectively.5.The residual amount of soil nitrate nitrogen increased with the increase of nitrogen application,while nitrogen reduction with straw returned to the field,nitrogen reduction with mixing different ratios controlled-release fertilizer and nitrogen reduction with adding different concentrations of nitrification inhibitor were reduced the residual amount of soil nitrate nitrogen and the leaching risk of soil nitrate nitrogen.After 3 years of experiment,compared with N250,N200 significantly reduced the nitrate nitrogen residue in soil profile(0-300cm)by 51.3%(p<0.05).After3 years of straw returned to the field,the nitrate nitrogen residue in soil profile(0-300cm)of N200+S was lower than N200,reduced by 18%(p<0.05);compared with N250,N250+S significantly reduced the nitrate nitrogen residue in soil profile(0-300cm)by 41.2%(p<0.05);compared with NC0,the treatments of nitrogen reduction with mixing different ratios controlled-release fertilizer significantly reduced the nitrate nitrogen residue in soil profile(0-300cm)by17.9%(NC65),27.1%(NC50)and 34.9%(NC35)respectively;compared with DCD0,the treatments of nitrogen reduction with adding different concentrations of nitrification inhibitor significantly decreased the nitrate nitrogen residue in soil profile(0-300cm)by 25.3%(DCD1)and 16.6%(DCD5)respectively. |
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