Characteristics Of Ammonia Volatilization From Farmland Of Major Grain Crops In China

Wheat,corn and rice,as the main grain crops produced in China’s farmland,are of vital importance to solving the problem of food and clothing for more than 1.3 billion people in China and ensuring China’s food security.Ammonia is an important substance for the formation of PM2.5,which can generally react with sulfur dioxide and nitrogen oxides to produce ammonium sulfate and ammonium nitrate,so reducing ammonia volatilization plays an important role in the treatment of PM2.5 pollution.On a large scale,while industrially planting wheat,corn,rice and other food crops,ammonia emissions will inevitably occur.Therefore,it is of great significance to explore the production of ammonia volatilization in China’s farmland during agricultural activities without reducing the yield of the three major food crops,which is of great significance to China’s agricultural development and its environmental and ecological improvement.This paper mainly collects and sorts out the results of field experiments carried out in China before 2022 at home and abroad,and uses the method of integrated analysis to evaluate the effects of nitrogen fertilizer use,fertilization methods,climatic conditions,soil properties,etc.on ammonia volatilization and possible mechanisms,and identify the more key influencing factors,so as to provide a scientific basis for the application of ammonia volatilization and emission reduction in grain crops in China.In this study,the results of field experiments published at home on the ammonia volatilization characteristics of grain crops in China’s farmland before 2022 were collected,and the Chinese literature was from"CNKI","Google Scholar","Wanfang"and"Weipu",and the English literature was from"Web of Science".The keywords are"ammonia emissions","ammonia volatilization","NH3 emission","ammonia","ammonia volatilization","corn","maize","wheat","wheat","rice","rice".By 2022,210 target literature and 1545 valid data had been screened out of the published literature on NH3 volatilization in China,and the effects of different climates（average annual temperature,average annual rainfall,climate type）,soil properties（p H,total N,organic carbon content）,management measures（nitrogen fertilizer amount,straw return,organic fertilizer type,fertilization method）on ammonia volatilization and yield of grain crops in China.The meta-analysis results indicate that:（1）There was no significant correlation between NH3 emissions,NH3 emission coefficient,NH3 emissions per unit yield,crop yield,and N application rate in farmland of the three major grain crops（wheat,corn,and rice）.（2）In temperate regions,with precipitation less than 1000mm and temperatures ranging from 5 to 15 degrees Celsius,the NH3 emission coefficient from wheat fields significantly decreases;In temperate regions,NH3 emissions from wheat fields have significantly decreased.Under acidic（p H<6.5）soil conditions,the amount and coefficient of NH3 emissions from wheat farmland significantly decreased;Under soil properties with a total nitrogen content greater than or equal to 2 g·kg^-1,the NH3emissions from wheat fields were significantly reduced;Under alkaline（p H>7.5）soil conditions,the NH3 emission coefficient from wheat farmland significantly decreased.Under the management measures of returning straw to the field,surface application,and adding slow-release fertilizers,the NH3 emissions and NH3 emission coefficient in wheat farmland were significantly reduced;Under the management measures of nitrogen fertilizer application ranging from 60 to 120 kg·hm^-2,deep application,and tillage,the NH3 emission coefficient of wheat farmland was significantly reduced.（3）Under climate conditions with precipitation greater than 1000mm,the NH3emissions and NH3 emission coefficients from corn farmland significantly decrease;Under the soil properties where the total nitrogen content is less than 2 g·kg^-1,the NH3emissions from corn fields are significantly reduced,and crop yields are increased;Under acidic（p H<6.5）soil conditions,the NH3 emissions from corn farmland were significantly reduced.Under the management measures of returning straw to the field and adding slow-release fertilizers,the NH3 emissions and NH3 emission coefficients of corn farmland were significantly reduced;Under the management measures of nitrogen fertilizer application ranging from 60 to 120 kg·hm^-2,the NH3 emissions per unit yield of corn farmland and crop yield significantly increased;Under the management measures of surface application,the NH3 emission coefficient of corn farmland has significantly decreased;Under the management measures of deep application,the NH3emissions from corn farmland have significantly decreased.（4）Under acidic（p H<6.5）and alkaline（p H>7.5）soil conditions,the yield of rice crops in agricultural fields has increased;Under soil properties with total organic matter greater than or equal to 20 g·kg^-1,NH3 emissions per unit yield and crop yield have increased.Under the management measures of surface application with a nitrogen fertilizer dosage greater than 240 kg·hm^-2,the NH3 emissions per unit yield of rice farmland and crop yield significantly increased;Under the management measures of returning straw to the field and nitrogen fertilizer dosage of 120-180 kg·hm^-2 and180-240 kg·hm^-2,the NH3 emissions per unit yield of rice farmland have increased;Under the management measures of adding slow-release fertilizers,the NH3emissions and NH3 emission coefficients from rice fields have significantly decreased;Under the management measures of returning straw to the field,the NH3emissions from rice fields have significantly decreased.In summary,in temperate regions,acidic（p H<6.5）soil conditions,straw returning to the field,surface application,and the addition of slow-release fertilizers are beneficial for reducing ammonia volatilization in wheat fields;When the precipitation is greater than 1000mm,the total nitrogen in the soil is less than 2 g·kg^-1,returning straw to the field,and adding slow-release fertilizers,it is beneficial to reduce ammonia volatilization in corn fields;Under the conditions of adding slow-release fertilizers,it is beneficial to reduce ammonia volatilization in rice fields.