The Influence of Aerated Irrigation on the Evolution of Dissolved Organic Matter Based on Three-Dimensional Fluorescence Spectrum

In order to unravel the effect of aerated irrigation on soil dissolved organic matter (DOM) fluorescence characteristics, and humification degree, a randomized block experiment was conducted with three factors and a two-level design, i.e., two irrigation rates (0.6 and 1.0 times of crop evaporation pan coefficient, W-1 and W-2), two nitrogen application rates (225 and 300 kg hm(-2), N-1 and N-2), and two aeration rates (15% and 0% in control treatment, A(1) and A(0)). Fluorescence regional integration (FRI) and correlation analysis methods were used to investigate the evolution characteristics of the soil DOM fluorescence spectrum. Under aerated and conventional subsurface irrigation, soil DOM components were dominated by humic acid-like substances, fulvic acid-like substances, tryptophan-like proteins, and supplemented by tyrosine-like proteins and dissolved microbial metabolites. Soil aeration could promote the consumption of soil DOM components under low irrigation rates and accelerate the consumption of soil DOM components under high irrigation rates. The humification index of AI treatments varied from 8.47 to 9.94 during the maturity growth stage of pepper, averagely increased by 31.59% compared with the non-aeration treatment. To sum up, aerated irrigation can promote the depletion of small molecular proteins and accelerate nutrient turnover and the accumulation of big molecular proteins.