Effects Of Water And Exogenous Organic Matter Regulation On Soil Carbon And Nitrogen Transformation

Returning exogenous organic matter to the field is an effective way to increase soil organic matter.The quality loss of exogenous organic matter is mainly through the immersion of dissolved organic matter(DOM)into soil.DOM is sensitive to external disturbances and can reflect the early potential changes of soil organic matter.At present,the regulatory effect and mechanism of the increase of soil soluble carbon DOM caused by the application of exogenous organic matter on the transformation of soil soluble carbon and nitrogen components have not been clarified.This limited the prediction of how soil carbon dynamics will respond to the return of exogenous organic matter to the field.In addition,the decomposition time of exogenous organic matter is long.Whether the decomposition process of exogenous organic matter can be reflected through soil monitoring by effective technical means and analytical methods has not been reported.The problems in these studies limit the popularization of the return of exogenous organic matter to field.Therefore,this paper first studied the response of greenhouse soil DOM,soluble carbon,soluble nitrogen,carbon cycle invertase and nitrogen cycle invertase under the application of different exogenous organic matter.Structural equation model and variation analysis were used to reveal the action path of soil major environmental factors on carbon and nitrogen invertase after the application of exogenous organic matter.Due to the lack of efficient decomposition of straw,three water gradients and two fertilizer application methods were set up to explore the responses of straw decomposition,DOM,soluble nitrogen and carbon nitrogen invertase under different water and fertilizer conditions.Convolutional neural network was used to extract the 3D fluorescence spectrogram features of DOM,and the working principle of the neural network was visually characterized by the gradient weighted class activation mapping method.This study is helpful to understand the nutrient turnover of soil after the application of exogenous organic matter,and promote the promotion of exogenous organic matter and the formulation of management strategies.The main results are as follows:(1)The application of exogenous organic matter increased the contents of soil soluble carbon,nitrate nitrogen,ammonium nitrogen and cellulase activity,among which the application of biochar increased the most.Compared with no fertilization,the application of exogenous organic matter was beneficial to the generation of nitrate nitrogen(path coefficient0.3).Humus-like components had the greatest effect on cellulase activity(path coefficient 0.67).(2)In the fast decomposition stage,DOM was mainly composed of protein-like substances,while in the slow decomposition stage,DOM was mainly composed of humus-like substances.When the irrigation amount was 60%～65% of the maximum field water holding rate,this conversion of soluble carbon components was promoted by applying biomass organic fertilizer.Convolutional neural network can identify this spectral feature of DOM in different decomposition periods(accuracy 97.5%).Compared with no fertilization treatment,when the irrigation amount was 70%～75% of the maximum field water holding rate,the increase of cellulase,urease,nitrate nitrogen and ammonium nitrogen was the largest under the combined application of biomass organic fertilizer treatment,and the promotion effect of soluble nitrogen component conversion was the most significant.