Effect Of Combined Application Of Manure And Chemical Fertilizer On Ammonia Volatilization In Citrus Orchard Soil

Ammonia（NH₃）can react in the atmosphere to form secondary aerosols and is a key factor in the formation of PM_2.5.When ammonia returns to the ground in the form of nitrogen deposition,it will cause a series of adverse effects on the environment such as soil acidification and water eutrophication.In China,fertilizer use contributes about half of NH₃emissions.In recent years,the citrus industry has developed rapidly,and the problem of excessive application of chemical fertilizers is common.The risk of NH₃ volatilization caused by this can no longer be ignored.Studies have shown that replacing chemical fertilizers with manure is can promote the efficiency and reduction of chemical fertilizers,but how the combination of manure and chemical fertilizers affect soil NH₃volatilization is still unclear.Therefore,this paper explores the effects of manure application and the application ratio of manure and nitrogen fertilizer on NH₃ volatilization in citrus orchard soil through field experiments and indoor cultivation experiments.At the same time,the differences in the effect of combined application of organic fertilizer and nitrogen fertilizer on NH₃ volatilization under different soil moisture and soil organic matter content were explored.The main findings are as follows:1.Soil NH₃ volatilization increased with increasing N application.NH₃volatilization increased by 41.74%,21.83%and 73.64%at the conventional fertilizer application（375.10kg N/ha）level compared to the reduced application of 30%N and 15%N fertilizer,and no N fertilizer application NH₃ volatilization,respectively.This was due to the significant increase in soil NH₄⁺-N content with increased N application.And the application of equal amount of organic fertilizer at each N application gradient increased NH₃ volatilization by7.40%-63.73%.This is because the organic fertilizer application significantly increased the soil NH₄⁺-N content and soil DOC content,thus promoting NH₃ volatilization.2.The NH₃ volatilization in orange orchard soil was mainly affected by air temperature,light,soil NH₄⁺-N content and soil DOC content.NH₃ volatilization was significantly positively correlated with air temperature and light,and was significantly positively correlated with soil NH₄⁺-N content and soil DOC content in partial correlation analysis.Temperature is the main factor affecting NH₃ volatilization in citrus orchard soil.3.In the indoor culture experiment,with the increase of soil moisture,the NH₃volatilization rate and the NH₃ volatilization accumulation amount decreased by 27.41%-35.53%in the nitrogen fertilizer only treatment.The increase of soil moisture can promote the nitrification of citrus orchard soil and the fixation of nitrogen by microorganisms,reduce the content of NH₄⁺-N in the soil,and reduce the volatilization of NH₃.4.The organic fertilizer application ratio of 25%and the addition of a small amount of organic fertilizer will significantly promote DOC decomposition,increase soil NH₄⁺-N concentration and soil p H,and promote NH₃ volatilization.The volatilization loss of NH₃was 14.4%-27.03%higher than that of nitrogen fertilizer only under suitable moisture content.Under suitable water content,when the organic fertilizer application ratio exceeds75%,the soil NH₃ volatilization rate and NH₃ volatilization accumulation will be significantly higher than those of the single nitrogen fertilizer treatment,and the organic fertilizer application ratio of 75%and 100%is higher than that of the nitrogen fertilizer only The cumulative amount of volatilization was 24.40%and 29.35%higher,respectively,and the NH₃ volatilization rate was significantly positively correlated with the CO₂emission flux.5.Soils with higher soil organic matter content had lower NH₃ volatilization when N fertilizer was applied in combination with organic fertilizer than those with low organic matter content.In soils with low organic matter content,NH₃ volatilization loss was reduced by 47.43%when organic fertilizer accounted for 25%of the total applied N compared to N fertilizer alone.When organic fertilizer accounted for 100%of the total N application,NH₃ volatilization loss was reduced by 79.46%compared to N fertilizer alone.6.In soils with low organic matter content,the urease activity at the beginning of incubation and organic nitrogen mineralization was significantly stronger than that in soils with higher organic matter content.And the organic fertilizer with nitrogen fertilizer will promote the microbial growth,uptake and utilization of NH₃ and reduce NH₃ volatilization in the soil with lower organic matter content.And in soils with high organic matter content,the microbial biomass of treatments with high percentage of organic fertilizer application was significantly higher than that of treatments with nitrogen fertilizer only.The stronger the correlation between soil NH₃ volatilization rate and CO₂ emission flux,the higher the accumulation of NH₃ volatilization,which indicates that soil organic matter and mineralization of newly applied organic fertilizer are important contributors to soil NH₃volatilization.