[Effects of Green Manures on Soil Dissolved Organic Matter in Moisture Soil in North China]

Soil dissolved organic matter (DOM) plays an important role in the biogeochemistry of carbon, nitrogen, and phosphorus and in the transport of heavy metals and pesticides in soil. In moisture soil, green manures and soils were sampled in situ at the ploughed stage of green manures. A 56-day laboratory incubation experiment was conducted to simulate the dynamic changes of soil DOM influenced by the decomposition of green manures, the green manures were Hairy vetch (Vicia villosa Roth.), February orchid (Orychophragmus Violaceus L.), Rye (Secale cereale L.), the soil without green manure was used as a control (CK). The composition and ultraviolet-visible spectrum parameters of soil DOM were investigated at different incubation stages. Results showed that green manures could increase the dissolved organic carbon (DOC), the total organic acids (TOAs) and total carbohydrate (TCs) contents, and all treatments were reached a peak on the 1st day and decreased later. Hairy vetch affected DOC and TOAs most and were increased by 114.01% and 109.10% higher than CK respectively at the 1st and 14th day. Rye influenced the total carbohydrate (TCs) most and was maximumly 323.18% higher than CK at the 42nd day. Green manures could increase the dissolved organic nitrogen (DON) content, DON in all green manure treatments increased on the 1st day, decreased several days later and increased again after 20～30 d. Hairy vetch effected DON best and was 305.83% higher than CK at the 42nd day. All green manures increased in SUVA254, SUVA260, SUVA272, SUVA280 and SAUC240-400, while decreasing in A250/A365 and A240/A420. The PCA analysis of ultraviolet-visible spectrum parameters showed that SUVA254, SUVA260, SUVA272, SUVA280 had a high positive correlation between each other, and the same situation was found between A250/A365 and A240/A420. Among them, SAUC240-400 was a key factor parameter featuring the characteristics of DOM. The results suggested that green manures could increase the contents of DOM and its aromaticity, hydrophobic percentage, humification degree and average molecular weight, and could be increased and the stability of DOM could be enhanced accordingly. The ultraviolet-visible spectrum parameters could indicate the changes of characteristics of DOM in this study.