长期施肥对稻田土壤镉锌铜积累及其有效性的影响

为明确长期不同施肥方式对稻田土壤Cd、Zn和Cu积累及其有效性的影响,以设立于1986年的长期定位施肥试验为对象,对比分析不施肥(CK)、单施化肥(NPK)、秸秆还田配施化肥(ST)、低量有机肥配施化肥(LM)、高量有机肥配施化肥(HM)5个处理耕层土壤重金属全量、有效态、形态分布以及水稻各部位重金属含量变化,结合土壤理化性质变化,探讨了长期施肥下重金属累积效应及其有效性变化机理。结果表明,NPK和ST处理对土壤全量及有效态Cd、Zn和Cu均无显著提高效应。而施用低量和高量有机肥30 a后,土壤Cd、Zn和Cu全量显著提高35.00%～80.00%、63.91%～82.55%、118.41%～180.21%,有效态显著提高28.57%～71.43%、407.12%～783.15%、336.59%～573.17%,稻米Cd、Cu则提高100.00%～150.00%、63.30%～85.64%。相关分析结果证实,有机肥中较高的重金属含量是造成稻田土壤Cd、Zn和Cu累积和有效性显著提高的主要原因,同时其改变的土壤理化性质,尤其是P也会影响重金属的有效性,但其作用机理有待深入研究。总体来看,长期施用有机肥具有更好的培肥效应,但会造成土壤Cd、Zn和Cu的富集以及稻米吸收量的增加,虽然目前稻米重金属含量尚未超出国家食品卫生标准限值,其风险仍不可忽视,在采取有机肥培肥土壤的过程中应严格控制其中的Cd、Zn和Cu等重金属含量。

Effects of long-term fertilization on accumulation and availability of Cd, Zn and Cu in paddy soil

To investigate the effects of long-term fertilization on accumulation and availability of Cd, Zn and Cu in a paddy soil, a field experiment was conducted since 1986. There were five treatments, including the control (no fertilizer, CK), chemical fertilizers (NPK), straw returning (ST), lower organic fertilizer (LM) and high organic fertilizer (HM) with similar N application rate. The total and available concentrations of cadmium (Cd), zinc (Zn) and copper (Cu) in the paddy soil and total concentrations of Cd, Zn and Cu in rice tissues were determined. Further, the relationships among the total and available concentrations of heavy metals in soil, the soil basic properties and the concentrations of heavy metals in brown rice were analyzed. The results indicated that the treatments of NPK and ST treatments have limited effect on accumulation of Cd, Zn and Cu in the soil. However, long-term application of organic fertilizers significantly increased soil total and available Cd, Zn and Cu by 35.00%~80.00%, 63.91%~82.55%, 118.41%~180.21% and by 28.57%~71.43%, 407.12%~783.15%, 336.59%~573.17%, respectively, as compared with the CK treatment. Compared to the CK treatment, the concentrations of Cd and Cu in brown rice of LM and HM significantly increased by 100.00%~150.00% and 63.30%~85.64%, respectively. Further, the correlations between soil total and available Cd, Zn, Cu and soil properties might indicated that the accumulation of heavy metals in soil was related to the high concentrations of Cd, Zn and Cu in organic fertilizer and the increase of soil total P could affect the availability of heavy metals in soil. In conclusion, long-term application of organic fertilizer can effectively improve the soil fertility, but could result in accumulation of Cd, Zn and Cu in the soil and subsequently in rice grain. Although, the concentrations of Cd and Cu in brown rice were lower than the limit standards of China, the risk enhancement of heavy metals in paddy soils should be paid more attention. When organic fertilizers were used to improve soil fertility, the concentrations of heavy metals in such fertilizers should be subject to careful control.