Effects of long-term fertilization on dissolved carbon leaching in lime concretion black soils

It is necessary to generate a sustainable strategy for evaluation of carbon leaching risk and organic fertilizer application by studying the effects of different fertilization practices on dissolved carbon leaching along soil profile in the area of lime concretion black soils. Aiming to analyze the contents and distribution of physicochemical, microbial properties, dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) contents in soil profile based on a 33-year long-term fertilization experiment to select an environmentally friendly organic amendments, five treatments were designed, including mineral fertilization (MF), mineral fertilization combined with low amount wheat straw (MFL), mineral fertilization combined with high amount wheat straw (MFH), mineral fertilization combined with pig manure (MFP), and mineral fertilization combined with cattle manure (MFC), respectively. Results showed that the contents of soil organic carbon, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in the profile at 0-60 cm soil depth were substantiality increased, whereas the values of soil total nitrogen, bulk density and pH value were mainly influenced at 0-20 cm soil depth in the organic amendments treatments compared with MF treatment. Compared with the MF treatment, soil DOC contents at 0-20 cm and >20-40 cm soil depths under long-term organic amendments application treatments were significantly (P<0.05) increased, whereas the values were not significantly increased at >40-60 cm soil depths. In contrast, soil DIC contents under long-term organic amendments application treatments at 0-60 cm depth were significantly (P<0.05) increased compared with the MF treatment. Both the values of UV280 absorption and aromaticity index (AI) at 0-60 cm soil depth were significantly (P<0.05) increased under long-term organic amendments application treatments, especially for the MFC treatment. The values of AI at the 0-20, >20-40, and >40-60 cm soil depths under the MFC treatment were significantly increased by 71.2%, 153.3%, and 38.1%, respectively. It was indicated that soil DOC chemical structure in the whole profile at 0-60 cm soil depth under long-term organic amendments application was greatly influenced and the contents of aromatic compound were increased, which suggested that soil DOC chemical structure under long-term organic amendments application were more complex. Furthermore, stepwise lineal regression showed that the DOC and DIC contents in the profile at 0-60 cm soil depth were regulated by soil pH value and MBC, and the strength of influence soil pH value was larger than soil MBC. Soil DOC chemical structure in the soil profile were mainly influenced by soil MBC. Generally, the type and amount of exogenous organic amendments were the two major factors influencing the characteristics of soil dissolved carbon distribution. The risk of dissolved carbon leaching was aggravated after long-term organic amendments application, especially for pig and cattle manure. Crop straw application is a recommended organic agricultural practice deceasing dissolved carbon leaching risk.