The Characteristics And Influencing Factors Of Soil Organic Nitrogen Fractions In Sediment Affected Area Of The Yellow River

Nitrogen is a limiting nutrient for plant growth and grain yield,and it is also an important index of soil fertility.Nitrogen forms are the basis of evaluating nitrogen availability,and organic nitrogen is the main component of soil nitrogen pool.Its structure and availability play a key role in soil nitrogen conservation,mineralization and supply.The lower reaches of the Yellow River is the main grain producing area in China,which plays an important role in grain production.However,soil fertility is low and excessive fertilization is common.Improving grain yield and nitrogen use efficiency has become the core issue of sustainable agricultural development in the lower reaches of the Yellow River.Therefore,this study takes Minquan County under the influence of sediment in the lower Yellow River as an example,through the steps of field sample collection,laboratory experiment,data processing and other steps,to analyze the characteristics of soil organic nitrogen fractions,soil physical chemistry properties and enzyme activities,and to explore the effects of land use on soil organic nitrogen fractions,Kriging interpolation was used to simulate the spatial distribution of soil organic nitrogen fractions,the main factors and relative contribution of soil organic nitrogen fractions in different locations of the region were investigated,and the relationships between soil organic nitrogen fractions and soil properties,elevation and precipitation were explored.In order to clarify the influence factors of soil organic nitrogen fractions in the sediment-affected area of the Lower Yellow River,and to provide theory and guidance for regional chemical fertilizer application and ecological environment improvement.The main conclusions are as follows:(1)The organic nitrogen fractions in 0-20 cm soil was mainly composed of non-hydrolysable nitrogen(276.67 mg/kg),hydrolysable ammonia nitrogen(108.23 mg/kg)and amino acid nitrogen(213.47mg/kg).The proportion of organic nitrogen fractions in total nitrogen varies from non-hydrolysable nitrogen,amino acid nitrogen,hydrolysable ammonia nitrogen,unknown nitrogen and amino sugar nitrogen.According to different land use types,the contents of total hydrolysable nitrogen,non-hydrolysable nitrogen,hydrolysable ammonia nitrogen and amino acid nitrogen in cultivated land were the highest,and the contents of organic nitrogen fractions in garden and forest land were in the middle level,the contents of total hydrolysable nitrogen,hydrolysable ammonia nitrogen,amino acid nitrogen,amino sugar nitrogen and hydrolysable unknown nitrogen were the lowest in wetland.The content of 0-20 cm was higher than 20-40 cm.(2)The spatial distribution trends of soil total hydrolysable nitrogen,non-hydrolysable nitrogen,hydrolysable ammonia nitrogen,amino acid nitrogen and hydrolysable unknown nitrogen are basically the same,the content of organic nitrogen fractions was higher in the east,where the cultivation intensity was high and the fertilizer application intensity was high,but the distribution of amino sugar nitrogen was not obvious.The spatial distribution of driving factors of soil organic nitrogen fractions showed that the driving factors of soil organic nitrogen fractions were different.Among them,soil chemical property was the dominant factor of total hydrolysable nitrogen(39.21%)and amino acid nitrogen(33.37%),soil enzyme activity was the dominant factor of non-hydrolysable nitrogen(35.65%),hydrolysable ammonia nitrogen(34.61%),amino sugar nitrogen(38.32%)and unknown nitrogen(34.66%).(3)Correlation analysis showed that total hydrolysable nitrogen,non-hydrolyzed nitrogen,hydrolysable ammonia nitrogen and amino acid nitrogen were positively correlated with soil total nitrogen and soil organic carbon,and negatively correlated with p H.Total hydrolysable nitrogen and hydrolysable ammonia nitrogen were positively correlated with catalase,sucrase,urease and alkaline phosphatase.The principal component analysis of soil organic nitrogen fractions and influencing factors showed that 12 environmental factors reduced to 3 principal components,and the cumulative variance contribution was67.36%.The variance contribution rate of the first principal component was 31.95%,which mainly included< 0.002 mm,0.002-0.02 mm,> 0.02 mm,total nitrogen and organic carbon.The variance contribution rate of the second principal component was 19.39%,it mainly includes < 0.002 mm,0.002-0.02 mm,> 0.02 mm,total nitrogen,catalase,sucrase.The variance contribution rate of the third principal component is 16.02%,this includes alkaline phosphatase,precipitation,and elevation.The results of multiple linear regression showed that total nitrogen,precipitation,invertase,organic carbon and < 0.002 mm were the best variables to explain total hydrolysable nitrogen;Total nitrogen,precipitation,organic carbon and sucrase were the best variables to explain non-hydrolysable nitrogen;Total hydrolysable nitrogen,sucrase and urease were the best variables to explain hydrolysable ammonia nitrogen;Total nitrogen,< 0.002 mm,sucrase and precipitation are the best variables to explain the amino acid nitrogen;Total nitrogen is the best variable to explain the amino sugar nitrogen;Total nitrogen,precipitation and organic carbon are the best variables to explain the hydrolysable unknown nitrogen.Path analysis showed that the comprehensive effects of environmental variables on total hydrolysable nitrogen from large to small were total nitrogen,precipitation,organic carbon,< 0.002 mm,invertase;The comprehensive effects of environmental variables on non-hydrolysable nitrogen were in the order of total nitrogen,organic carbon,invertase and precipitation;The comprehensive effects of environmental variables on hydrolysable ammonia nitrogen were ranked as total nitrogen,urease and sucrase;The comprehensive effects of environmental variables on amino acid nitrogen were ranked as total nitrogen,sucrase,precipitation and < 0.002 mm;Total nitrogen,precipitation and organic carbon were the order of the comprehensive effects of environmental variables on the hydrolysable unknown nitrogen.