Effects Of Maize Straw Returning And Nitrogen Management On Soil Nitrogen Components And Nitrogen Fertilizer Use Efficiency

Maize is an important grain crops in our country.In 2020,the maize yield in Heilongjiang accounted for 13.99%of the national total,the straw yield reached 43.759 million t（grain-grass ratio 1:1.2）,due to the lagging in the development of straw returning technology,the open burning of straw has caused severe air pollution.Maize returning straw to the field can solve the straw surplus problem,increase soil nutrients and ensure soil nitrogen storage.Nitrogen components in soil is closely related to crop yield,and both nitrogen application and straw return will affect soil nitrogen components content.The high C/N value of maize straw can lead to slow decomposition after return to the field,causing competition for nutrients between soil microorganisms and maize in the early stages and affecting maize growth and yield.Excessive nitrogen fertilizer application will result in greater expenses and decreased nitrogen use efficiency,whereas rational nitrogen fertilizer application is a vital strategy to boost production and income.Therefore,it is important to study the effect of maize straw returning and nitrogen fertilizer management on soil nitrogen components and nitrogen fertilizer efficiency,and provide theoretical basis for scientific implementation of straw returning and reasonable use of nitrogen fertilizer.The experiment were carried out continuous positioning with frame planting and ¹⁵N tracking method in the campus test base of Northeast Agricultural University in 2021.The experiment were set up with three nitrogen fertilizer application rates under maize straw returning（S1）and no straw returning（S0）conditions,with 0.00g,1.24 g(175 kg·ha^-1)and 2.48 g(350 kg·ha^-1)of urea（N:46%）applied to ¹⁵N label（abundance:3.603%）per frame,respectively,and with the base fertilizer and top dressing ratio of 1:0 and the base fertilizer and top dressing ratio of 1:1 two forms of nitrogen fertilizer application to determine the variation of soil nitrogen components,maize nitrogen absorption and nitrogen fertilizer efficiency under the conditions of maize straw returning with nitrogen fertilizer.The results showed that:（1）Continuous maize straw returning,nitrogen application rate,and base dressing ratio had significant effects on soil available nitrogen content.Continuous return of straw to the field for 5（before sowing）and 6（after harvest）years increased soil available nitrogen content,which of each nitrogen application treatment showed that the straw returning（S1）was higher than the no straw returning（S0）treatment,the soil NO₃^--N content also showed S1>S0,but the NH₄⁺-N content showed S1<S0,reaching a significant level between treatments;soil available nitrogen content increased with increasing nitrogen treatment rate before seeding and after harvest under both straw returning and no straw returning conditions,the no top dressing fertilizer was higher than top dressing fertilizer treatment,and the change rules of soil NH₄⁺-N and NO₃^--N were consistent with soil available nitrogen（2）Continuous maize straw returning,nitrogen application rate,and base dressing ratio had significant effects on soil total nitrogen,acid hydrolyzed total nitrogen,acid hydrolyzed ammonia nitrogen,amino sugar nitrogen,amino acid nitrogen,unknown nitrogen,non-acid hydrolyzed nitrogen and microbial nitrogen content.Continuous return of straw to the field for 5 years increased the contents of each index of soil nitrogen components,which of each nitrogen application treatment showed that S1>S0,reaching a significant level between treatments.Under the conditions of straw returning and no straw returning,with an increase in nitrogen application rate,each index of soil nitrogen components content increased,the no top dressing fertilizer was higher than top dressing fertilizer treatment,while the no top dressing fertilizer of soil microbial nitrogen content was lower than top dressing fertilizer treatment when the urea application rate was 350kg·ha^-1.（3）Continuous maize straw returning,nitrogen application rate,and base dressing ratio had significant effects on nitrogen accumulation in maize plants.The nitrogen accumulation at seedling and jointing stages was decreased by continuous straw returning,which showed S1>S0 for each nitrogen application treatment,whereas the nitrogen accumulation at harvest stage showed S1>S0for each nitrogen application treatments,reaching a significant level between treatments,the nitrogen accumulation of maize at seedling stage,jointing stage,and harvest stage increased with increased nitrogen application under both straw returning and no straw returning conditions,and no top dressing fertilizer at seedling stage and jointing stage was higher than top dressing fertilizer treatment,the change law of the harvest stage was opposite to that of the seedling and jointing stages.（4）Continuous maize straw returning,nitrogen application rate,and base dressing ratio had significant effects on nitrogen fertilizer use efficiency.Continuous straw returning reduced nitrogen fertilizer use efficiency of maize,which of each nitrogen application treatment was showed S1<S0.Under both straw returning and no straw returning conditions,and the no top dressing fertilizer was lower than top dressing fertilizer treatment.（5）Continuous maize straw returning,nitrogen application rate,and base dressing ratio had significant effects on yield.Continuous maize straw returning increased the yield,which of each nitrogen application showed S1>S0,the yield of maize increased as the nitrogen application rate was increased under both straw returning and no straw returning conditions,and the no top dressing fertilizer was lower than top dressing fertilizer treatment.（6）Continuous maize straw returning and nitrogen application can significantly increase soil nitrogen content,promote nitrogen accumulation in plants,and increase maize yield;The base dressing ratio did not promote the increase of soil nitrogen content,but it could increase the nitrogen accumulation and yield of maize plants at the harvest stage.