Spectral Analysis of the Effect of Organic Fertilizer Application on the Evolution of Organic Matter and Nitrogen in Farmaland

Organic fertilizer is an effective means to improve soil physical structure, enhance soil fertility and regulate nutrient balance. However, the effects of organic fertilizer application on the evolution of organic matter and nitrogen in farmland are still unclear. This paper studied the changes of TOC, DOC and inorganic nitrogen contents in soil after applying organic fertilizer. The changes of DOM spectral characteristics of soil after applying organic fertilizer were analyzed using three-dimensional fluorescence spectroscopy. PARAFAC was used to analyze the changes in the relative contents of the fluorescent components in soil DOM in different periods after applying organic fertilizer, and 2D-COS was used to analyze the change sequence of the fluorescent components with time. In addition, the response relationship between the relative content of DOM components and soil nitrogen was studied using the typical correlation analysis method to explore the effects of organic fertilizer application on the evolution of soil organic matter and nitrogen. The results showed that : (1) The application of organic fertilizer increased the content of total organic carbon, water-soluble organic carbon and nitrate nitrogen but decreased the content of ammonium nitrogen. (2) Three-dimensional fluorescence spectra of soil DOM showed a peak (UV humic acid) , M peak (UVA humic acid) and T peak (tryptophan). PARAFAC analysis showed that soil DOM was mainly composed of terrestrial humic acid (C1) , typical humic acid (C2) and tryptophan (C3). The results showed that applying organic fertilizer could increase the relative contents of soil C1 C2 and C3 components. The relative contents of C1, C2 and C3 in the soil treated with organic fertilizer increased initially and then decreased, reaching the maximum on the 30th day. The change order of different fluorescence components with time was C1(C2) up arrow -> C3, and humic acid-like changed greatly, and the promotion of humic acid-like by organic fertilizer was significant. (3) The application of organic fertilizer can improve the bioavailability of soil and reduce the degree of soil humification. BIX value increased first and then decreased after applying organic fertilizer and reached the maximum on the 30th day; The HIX value decreased at first and then went up and reached the minimum on the 30th day. BIX and HIX were negatively correlated (R-2 =0. 732). (4) The relative contents of C1 C2 and C3 were positively correlated with nitrate nitrogen and negatively correlated with ammonium nitrogen, and the relative contents of C1 and C2 had a great influence on the contents of nitrate nitrogen and ammonium nitrogen. In conclusion, reasonable application of organic fertilizer can control the transformation of soil organic matter and nitrogen reducing the non-point source pollution of chemical fertilizer.