Dynamics And Profile Differentiation Of Soluble Organic Nitrogen Components In Paddy Soil After Application Of Chinese Milk Vetch

Soluble Organic Nitrogen?SON?is an important nitrogen component in soil ecosystems.It is composed of nitrogen-containing compounds with different structures and the components with smaller molecular weights such as Free Amino Acid Nitrogen?FAA-N?,Soluble Protein Nitrogen?SP-N?,Amide Nitrogen?A-N?and other substances that can be directly absorbed by plants and microorganisms.In addition,SON is also the main form of nitrogen loss in soil,the migration ability of SON is different due to the different chemical properties of nitrogen-containing compounds in SON.Chinese Milk Vetch is a common green manure crop in the southern region of China.A large amount of Chinese Milk Vetch applied to the soil will inevitably produce a large number of SON,while increasing the arable land these SON are likely to migrate and leach down,leading to non-point source pollution of farmland ecosystems.However,the dynamic changes and mechanism of SON in paddy soil during rice growth period after application of Chinese Milk Vetch is still unclear,moreover,research on the environmental risk of the application of Chinese Milk Vetch on the migration and leaching of SON components in paddy soil is even rarer.To this end,this study took the typical paddy soil?stucco field?in the subtropical region as the research object,and set up field positioning experiments of different amounts of Chinese Milk Vetch in the wild.The experiment set up three kinds of fertilization treatment,single application of chemical fertilizer?CK?,medium amount of Chinese Milk Vetch(application rate30000 kg Vetch(application rate 45000 kg hm^-2)+chemical fertilizer?CMV2?.The dynamic changes and mechanism of SON composition in the plough layer?0-20 cm?soil of paddy field under turning over different amounts of Chinese Milk Vetch during the rice growth period were investigated by various modern analysis technologies such as carbon and nitrogen element analyzer,total organic carbon analyzer with nitrogen detector,continuous flow analyzer,automatic amino acid analyzer and Fourier infrared spectrometer.Revealing the migration and differentiation of SON components in the soil profile?0-60 cm?during rice growth period.To explore the main controlling factors for the dynamic changes of SON composition in the stucco field after turning over Chinese Milk Vetch.Provide scientific basis for elucidating the chemical nature and ecological function of each component of soil SON in paddy field ecosystem,formulating a reasonable application plan of Chinese milk vetch,and preventing and controlling nitrogen migration in farmland.Research indicates:?1?The content of FAA-N in the topsoil of Chinese Milk Vetch treatment during the growth period of rice is as follows:heading and flowering period>mature period>tillering period>transplantation period>seedling stage;compared with single fertilizer treatment.The pressure treatment can increase the FAA-N content of the paddy soil in paddy fields to varying degrees,and the FAA-N content of the cultivated soil with the high amount of Chinese Milk Vetch turned over is the most obvious.?2?The composition of FAA-N in paddy soil of different fertilization treatments during the rice growth period is different,but these are mainly neutral amino acids?88.30%-99%?,followed by acidic amino acids?1.00%-9.18%?,The basic amino acids?0.00%-5.27%?are the least;the FAA-N in paddy soil of different fertilization treatments are creatine,glycine,alanine,valine,isoleucine,leucine and phenylalanine.The content of amino acid is relatively high,accounting for 69.42%-85.58%of the total FAA-N.Chinese Milk Vetch pressure treatment can enrich the FAA-N types and increase the content of each amino acid component in the topsoil compared with single fertilizer treatment.The growth of rice also has a certain effect on the content and composition of FAA-N in the topsoil.The heading and flowering period is the most abundant period of FAA-N species in the topsoil with different treatments,and the content of each amino acid component is also relatively high.?3?The SP-N content and the SP-N/SON ratio of the plow layer treated by Chinese Milk Vetch during the rice growth period showed a trend of first increasing and then decreasing.The heading and flowering stage is the period when the SP-N content of the topsoil treated by Chinese Milk Vetch is the highest,The period with the highest SP-N content is the tillering period and the heading and flowering period are periods with a relatively high SP-N/SON ratio.Compared with the single application of chemical fertilizer treatment,Chinese Milk Vetch treatment can significantly increase the SP of cultivated soil-N content,and the soil SP-N content increases with the increase of the application amount of Chinese Milk Vetch.?4?The A-N content in the plow layer soil of Chinese Milk Vetch treatment and single application of chemical fertilizers during the rice growth period showed an"M"-type change trend.The application of chemical fertilizers in the paddy field can quickly increase the A-N content of the topsoil,and the treatment of Chinese Milk Vetch can increase the A-N content of the topsoil in the middle and late stages of rice growth,the content increase is most significant.?5?The contents of large molecular weight SON,such as phenols,alcohols,aliphatic compounds and carbohydrates?monosaccharides,polysaccharides and carbohydrate derivatives?,in the paddy field used after Chinese Milk Vetch application were reduced.However,the reduction of carbohydrates was the largest.Most of organic nitrogen compounds with larger molecular weight in the topsoil in the treatment of Chinese Milk Vetch after the rice seedling stage were increased first and then decreased.The tillering period and the heading and flowering period are periods when the content of nitrogen-containing compounds such as phenols,alcohols,aliphatic compounds,aromatic compounds,and carbohydrates in the topsoil is high;The treatment can increase the content of large molecular weight SON?phenols,alcohols,aromatic compounds,carbohydrates,etc.?in the soil of the plough layer more than the chemical fertilizer treatment alone.?6?The FAA-N content of the soil at the seedling stage and the heading and flowering stage decreases with the increase of the soil depth,and it shows obvious vertical distribution characteristics in the soil profile.The soil FAA-N has a downward migration trend in the soil layer,mainly migrated to 20-40 cm soil layer;Chinese Milk Vetch pressure treatment has different effects on soil FAA-N content at different depths.With the increase of soil depth,the effect of Chinese Milk Vetch pressure treatment on soil FAA-N content gradually decreases.The ratio of FAA-N to SON in the 20-40 cm and 40-60 cm soil layers in the seedling stage and the heading and flowering stage were higher than that of the single fertilizer application,which further showed that the treatment of Chinese Milk Vetch could promote FAA-N migrates to the lower soil layer.?7?The FAA-N in the soil at the seedling stage and the heading and flowering stage?20-40 cm and 40-60 cm?are neutral amino acids,of which the content of sarcosine is highest;methionine,hydroxyproline,asparagine.threonine,serine and glycine are the main components of the FAA-N difference in different soil layers of the fertilization treatment of the paddy field at the seedling stage and the heading and flowering stage.The treatment of high-volume Chinese Milk Vetch can increase the FAA-N species in the 0-20 cm and 20-40 cm soil layers at the seedling stage compared with the single chemical fertilizer treatment.?8?The SP-N content of the soil at the seedling stage and the heading and flowering stage decreased with the increase of the soil depth,and showed obvious vertical distribution characteristics in the soil profile.The ability of the soil SP-N to migrate downward in the tested paddy soil was weak,mainly concentrated in the 0-20 cm soil layer.The ratio of SP-N to SON in the 20-40 cm and 40-60 cm soil layers of Chinese Milk Vetch overturning treatment is higher than that of single fertilizer application.?9?The A-N content of the soil at the seedling stage and the heading and flowering stage decreased with the increase of the soil depth,and showed obvious vertical distribution characteristics in the soil profile.The effect of increasing the content of A-N in the 20-40 cm and 40-60 cm soil layers is significantly higher than that in the 0-20 cm soil layer,indicating that A-N is easy to migrate downward in the paddy soil.Chinese Milk Vetch 20-40 cm and 40-60 cm soils are treated in the seedling and heading stage.The ratio of A-N to SON in the layer is higher than that of single fertilizer application,which further indicates that turning over Chinese Milk Vetch can promote the A-N migration of paddy soil.