长期施磷稻田土壤磷素累积及其潜在环境风险

Soil phosphorous accumulation in long-term P fertilization paddy field and its environmental effects

应用常规化学分析法和数学统计方法,基于太湖地区13年的长期定位试验,研究长期不同施磷水平下[0（不施磷）、30 kg.hm 2.a 1（低磷）、60 kg.hm 2.a 1（适磷）、90 kg.hm 2.a 1（高磷）]稻麦轮作系统稻田土壤磷素累积规律及磷素流失引发的环境风险。在本试验区土壤环境条件下,可能发生稻田磷素淋溶及径流的土壤耕层（0~15 cm）Olsen-P临界值分别为26.0 mg.kg 1和24.8 mg.kg 1。连续13年适磷、高磷施肥,土壤耕层Olsen-P含量分别达到26.9 mg.kg 1和33.2 mg.kg 1,均高于临界值浓度,且已导致稻田田面水与30 cm渗漏水中总磷浓度显著升高,大大提高了稻田磷素淋溶及径流的风险。低磷施肥土壤Olsen-P长期稳定在（10.1±2.0）mg.kg 1水平,并且每年的稻麦产量与高磷、适磷处理相比并无显著差异,而长期低磷施肥土壤磷的流失风险也较小。因此,在太湖地区稻麦轮作体系下,磷肥不宜以常规适磷水平长期施用,建议以低磷水平（30 kg.hm 2.a 1）长期施用或以适磷水平（60 kg.hm 2.a 1）间歇式施用。

The continuous and excessive application of phosphorus（P） fertilizers and manure in intensive agricultural systems have led to soil P accumulation and progressive saturation of soil sorption capacity.This has significantly influenced soil P loss and P accumulation in aquatic ecosystems.The Taihu Lake Region of the Yangtse River Delta has for decades been a highly intensive agricultural production zone in China.Here,applications of chemical fertilizers and farmyard manure have been an effective method of improving soil fertility and productivity.Long-term applications of fertilizers and/or manure,often in excess of immediate plant uptake,have resulted in significant P accumulation and loss in this region.This has considerably increased the potential for eutrophication in the Taihu Lake.The change-point theory（with a soil Olsen-P content threshold above which the potential for significant P loss from soils to water systems occurred） has been considered to be scientific and useful in P management in agricultural soils.Up to date,however,there has been less report with respect to the Olsen-P change-point theory for paddy soils in the Taihu Lake Region.In this study,a long-term（13 years） P fertilization experiment in four P application doses（0 kghm2a·1,30 kghm2a·1,60 kghm2a·1 and 90 kghm2a·1） was conducted in the Taihu Lake Region to evaluate the accumulation of Olsen-P under rice-wheat rotation cropping system.The experiment evaluated the environmental risks caused by P loss from soils to water systems.Topsoil（0~15 cm）,surface water and leachates（30 cm and 60 cm） Olsen-P and total P（TP） contents were determined.Furthermore,a split-line regression model was used to estimate the risks of P loss from soils to water bodies and the change-point of soil Olsen-P in the Taihu Lake Region determined.Although,TP concentrations in surface water bodies and in 30 cm leachate significantly increased with increasing application rate of fertilizer-P,no significant increase was observed in the 60 cm leachate.As the risk of P runoff was mainly in the first 9 days after fertilizer-P application,it was advisable to control paddy field drainage during this period.Split-line regression analysis suggested that the change-points of Olsen-P content in surface soil triggering P leaching and runoff were respectively 26.0 mg·kg·1,24.8 mg·kg·1.Fertilizer-P application at 60 kghm2a·1 and 90 kghm2a·1 for 13 years resulted in respective soil Olsen-P accumulation of 26.9 mg·kg·1 and 33.2 mg·kg·1,which were all higher than the change-points.TP concentration of 30 cm leachate was also increased significantly.With continuous application of fertilizer-P at 30 kghm2a·1 for 13 years,soil Olsen-P content remained at（10.1±2.0） mg·kg·1.This was sufficient for optimum rice/wheat growth without any risk of P loss.It was therefore not suitable to continuously apply 60 kghm2a·1 of fertilizer-P for a long time in paddy fields.The results demonstrated that intermittent fertilizer-P applications at 30 kghm2a·1 and 60 kghm2a·1 were suitable for rice-wheat rotation cropping system in the Taihu Lake Region.