Changes of organic carbon and nutrient contents in highly productive paddy soils in Yujiang County of Jiangxi Province

Chinese. 研究高产水稻土有机碳和养分含量变化状况，为水稻土的定向培肥和持续利用提供科学参考。通过田间采样分析并比较第二次土壤普查的背景资料，研究江西省余江县高产水稻土有机碳和养分的含量状况及其近20余年来的变化情况，并分析其环境意义。江西省余江县高产水稻土表层0～10 cm的有机碳、全氮和速效磷含量分别为（20.2±3.88）g/kg、（2.09±0.55）g/kg、（42.7±32.7）mg/kg，均达到非常丰富的水平。近20余年来土壤有机碳库基本保持稳定、处于平衡状态，但全氮和速效磷含量显著增加，而速效钾含量变化不明显。高产水稻土表层0～10 cm的磷固定量和固定率分别为（142.7±41.1）mg/kg和（36.2±10.4）%，CEC为（7.93±1.32）cmol/kg，并不比一般水稻土和旱地红壤高。这使通过施肥进入土壤的磷活动性增加，以致更易进入水体，可能是区域水体富营养化的主因。经过长期的耕作培肥，高产水稻土的有机质和速效磷含量均达到非常丰富的水平，有机碳库基本处于平衡状态，但磷的固定量并不高。由于该类型土壤的固钾能力较弱，高产水稻土的速效钾含量并不丰富，应当重视钾库的平衡保持和提高。

English. Studies on changes in organic carbon and nutrient contents of the highly productive paddy soils would be scientifically beneficial to the directional management and sustainable utilization of paddy soils. The contents of organic carbon and nutrients and their changes in the last over 20 years in the highly productive paddy soils as related to the environmental significance were investigated by field sampling and comparison with the corresponding values in the Second Soil Survey in Yujiang County of Jinagxi Province. Results showed that 0-10 cm depth highly productive paddy soils in Yujiang County of Jiangxi Province contained organic carbon content of (20.2±3.88) g/kg, total N (2.09±0.55) g/kg, available phosphorus (42.7±32.7) mg/kg, respectively, all were at the very rich level. In the last over 20 years, the organic carbon pool of the highly productive paddy soils remained a stable state, total N and available P increased significantly, while available K changed little. The amount and percentage of P immobilized in 0-10 cm highly productive paddy soils were (142.7±41.1) mg/kg and (36.2±10.4)% and of added P CEC was (7.93±1.32) cmol/kg, being not higher than the mean value of paddy soils and that in upland red soils. It indicated that fertilizer P in highly productive paddy soils would be a high mobility and easily moved to water, being a main source of nutrient causing eutrophication. For a long-term rice cultivation and fertilization, the highly productive paddy soils were very rich levels of organic matter and available P, and a steady state of organic carbon pool, while amount of P immobilized was not high. Because of a weak K-fixing capacity, the available K content was not rich in highly productive paddy soils, suggesting that attention should be paid to the balance and increase of soil K pool.