Soil aggregates and organic carbon affected by the land use change from rice paddy to vegetable field

Abstract

Land use changes can influence soil organic carbon (SOC) and other properties significantly. The aim of this study was to investigate the effect of paddy conversion to vegetable field on organic carbon and soil structure. Samples of soil and plant residue were collected from paddy fields and vegetable fields converted from paddy for over 20 years. Results showed that the SOC content and density decreased 19.68% and 0.4kg/m2 after the land use change. The decrease of soil carbon was mainly attributable to the loss of particulate organic carbon (0.35kg/m2). Compared to the paddy field, 14.01% of water-stable macro-aggregates were broken into micro-aggregates in the vegetable field, resulting in the mean weight diameter of aggregates and the percentage of aggregate destruction were about 71.5% and two times, respectively. The organic carbon content associated with water-stable macro-aggregates was higher than that with micro-aggregates (12.2–16.4 vs. 12.0–12.4g/kg). The organic carbon content associated with water-stable macro-aggregates in the paddy soil was higher than that in the vegetable field soil (16.4–15.0 vs. 13.1–12.2g/kg). Therefore, the total soil organic carbon density decreased due to the land use conversion. The decrease of root biomass and plant residue returning and the excessive inorganic nitrogenous fertilizer application resulted in the microbial carbon content decrease of 37.5%. The information from this study should be useful to understand changes of soil properties and soil carbon sequestration with the land use conversion.