中文摘要：

通过田间采样结合沉降法分级提取，研究了不同利用年限红壤水稻土有机碳和养分含量的粒级分布变化特征。结果表明，红壤水稻土有机碳和养分含量随土壤颗粒粒径的增大而下降，但在各粒级中的分布比例存在显著差异。〈0．002mm、0．002—0．02mm、0．02～0．05mm、〉0．05mm粒级的有机碳占全土有机碳的比例分别是29．2％、30．7％、11．9％、15．4％，氮的相应数值为36．7％、31．9％、10．2％、14．0％，磷为49．2％、26．5％、11．1％、12．4％，钾为36．9％、33．4％、12．9％、20．0％。总体来说，黏粒和粉粒中有机碳和养分的分布比例较高。红壤水稻土有机碳和养分含量及分布比例还随利用年限而有明显变化。开垦利用不到10a的水田土壤，有机碳和养分含量较低且主要集中在〈0．002mm粒级中；而利用超过10a的水稻土，有机碳和养分在粉粒中（0．002～0．05mm）的比例大于50％。各利用年限的红壤水稻土多以0．02～0．05mm粒级的C／N为最高，并随利用年限延长而下降。红壤水稻土各粒级有机碳和养分含量及分布状况随利用年限的变化反映了土壤肥力熟化和养分有效性的提高过程。

英文摘要：

Change in distribution of C, N, P and K in particle-size fractions of a cultivation chronosequence of paddy soils in subtropical China was investigated by particle-size fractionating with the sedimentation method. Results show that contents of organic C, N, P and K in various fractions decreased with increasing particle size, and that their distribution in the fractions varied significantly in percentage. Organic Carbon in fractions of 〈 0. 002 mm, 0. 002 - 0.02 mm, 0.02-0.05 mm and 〉0.05 mm accounted for 29.2%, 30.7%, 11.9% and 15.4%, N for 36.7%, 31.9%, 10.2% and 14.0%, Pfor49.2%, 26.5% , 11.1% and12.4%, and K for 36. 9% , 33.4%, 12.9% and 20.0%, respectively of the total in the soil. Generally, a high percentage of organic C, N, P and K was distributed in clay and silt as well. Besides, their distribution in the fractions differed obviously with the cultivation history of paddy soils. In paddy fields less than 10 years in rice cultivation, the contents of soll organic C, N, P and K were relatively lower and mainly distributed in Fraction 〈0. 002 mm, whereas in paddy fields more than 10 years in rice cultivation, the distribution of organic C and nutrients in silt （0. 002 -0.05 mm） exceeded 50%. Silt （0.02 -0.05 mm） was also the highest in C/N ratio regardless of cultivation history, but it did decrease with rice cultivation going on, which suggests that the observed changes indicate improvement of soil fertility and soil nutrient availability.