Changes in Soil C and N Contents and Mineralization Across a Cultivation Chronosequence of Paddy Fields in Subtropical China

摘要

Dynamics of soil organic matter in a cultivation chronosequence of paddy fields were studied in subtropical China.Mineralization of soil organic matter was determined by measuring CO2 evolution from soil during 20 days of laboratoryincubation. In the first 30 years of cultivation, soil organic C and N contents increased rapidly. After 30 years, 0-10 cmsoil contained 19.6 g kg-1 organic C and 1.62 g kg-1 total N, with the corresponding values of 18.1 g kg-1 and 1.50g kg-1 for 10-20 cm, and then remained stable even after 80 years of rice cultivation. During 20 days incubation themineralization rates of organic C and N in surface soil (0-10 cm) ranged from 2.2% to 3.3% and from 2.8% to 6.7%,respectively, of organic C and total N contents. Biologically active C size generally increased with increasing soil organicC and N contents. Soil dissolved organic C decreased after cultivation of wasteland to 10 years paddy field and thenincreased. Soil microbial biomass C increased with number of years under cultivation, while soil microbial biomass Nincreased during the first 30 years of cultivation and then stabilized. After 30 years of cultivation surface soil (0-10 cm)contained 332.8 mg kg-1 of microbial biomass C and 23.85 mg kg-1 of microbial biomass N, which were 111% and 47%higher than those in soil cultivated for 3 years. It was suggested that surface soil with 30 years of rice cultivation insubtropical China would have attained a steady state of organic C content, being about 19 g kg-1.