红壤稻田土壤有机质的积累过程特征分析

通过田间采样分析 ,研究了不同利用年限红壤稻田土壤有机质含量的变化及其过程和机理 ,确定达到平衡状态时红壤稻田土壤的有机碳含量水平。结果表明 ,在水耕条件下 ,土壤有机碳和全氮的积累过程可大致分为快速增长和趋于稳定阶段 ,水耕利用 30年 ,0～ 2 0cm土壤有机碳含量达到 2 0gkg- 1,全氮含量 1 6gkg- 1,随后 ,即使利用年限长达 80年 ,土壤有机碳和全氮含量变化趋于稳定 ,没有显著提高。 2 0天的培养期内 ,不同利用年限红壤稻田 0～ 1 0cm土层有机碳和有机氮的矿化率分别为 2 2 %～3 3%和 2 8%～ 6 7% ;总体来说 ,有机碳、氮的矿化率随红壤水稻土的熟化过程而升高。随着利用年限的增加 ,微生物生物量碳一直保持增加的趋势 ,而微生物生物量氮在利用 30年后其增加趋势明显趋缓 ;利用30年的红壤稻田 ,0～ 1 0cm土壤微生物生物量C、N为 332 8mgkg- 1和 2 3 85mgkg- 1,比利用 3年分别高1 1 1 %和 4 7%。与利用 3年的红壤稻田相比 ,利用 30年后细菌数量增加了 1 1倍 ( 0～ 1 0cm)和 3 8倍 ( 1 0～2 0cm) ,利用 80年后更显著地增加了 1 9倍 ( 0～ 1 0cm)和 1 2倍 ( 1 0～ 2 0cm) ;真菌的数量也呈上升的趋势 ,但在 30年利用后基本趋于稳定 ;此外 ,细菌的群落从荒草地的 4个种到 30～ 80年水田

SOIL ORGANIC MATTER DYNAMICS IN A CULTIVATION CHRONOSEQUENCE OF PADDY FIELDS IN SUBTROPICAL CHINA

Organic matter is an important soil component that influences the physical, chemical and biological properties of soils.Maintenance of its content in the soil has been the crucial measure for improving productivity and stabilizing ecosystems.Stabilization of the organic matter also plays a pivotal role in controlling global warming through an increasing sequestration of atmospheric CO₂ to the plant-soil system.In this paper, dynamics and processing mechanisms of soil organic matter accumulation for a cultivation chronosequence in paddy field were studied in subtropical China by sampling in field, and determining steady-state soil C contents.Under paddy cult ivation, soil organic C and N increased rapidly for 30 years, leveling off thereafter.After 30 years of rice planting with irrigation, 0~20 cm soil organic C and N increased to 20 g kg^-1 and 1.6 g kg^-1, respectively, and then insignificantly changed even through 80 years of utilization.During 20 days' incubation, the mineralization rates of 0~10 cm soil organic C and N in a cultivation chronosequence of paddy field ranged from 2.2%~3.3% and 2.8%~6.7%, which in general increased with soil organic C and N contents.Soil microbial biomass C increased proportionately with cultivation years, in comparison, the soil microbial biomass N increased in the first 30 years and then leveled off.0~10 cm soil cultivated as paddy field for 30 years has a 332.8 mg kg^-1 of microbial biomass C and 23.85 mg kg^-1 microbial biomass N, which were 111% and 47% higher than that for paddy field cultivated for 3 years.The numbers of bacteria in the soil cult ivated as paddy field for 30 years were 1.1-fold (0~10 cm) and 3.8-fold (10~20 cm) higher than that for 3 years, and the corresponding values in soils cultivated for 80 years were 19-fold (0~10 cm) and 12-fold (10~20 cm).The number of fungi was also increased in the first 30 years' cultivation and then leveled off.Furthermore, the increasing community of bacteria from 4 in wasteland to 8 in paddy soil under 30~80 years of cultivation indicated the improvement of soil fertility.