长期施用猪粪和化肥对稻田土壤Cu、Zn和Cd含量及有效性的影响

为研究有机肥与化肥处理下稻田土壤Cu、Zn、Cd含量之间的差异，并探明关键影响因子，本研究利用持续了35 a的长期定位试验，分析了土壤重金属全量及有效态、土壤理化性质和水稻产量，并利用多种统计分析方法研究了猪粪组和化肥组土壤Cu、Zn和Cd与土壤理化指标之间的关系。结果表明：与对照（不施肥）相比，长期施用猪粪使土壤Cu、Zn、Cd全量和有效态含量分别提高了134%~239%、57%~124%、58%~171%和191%~380%、285%~811%、61%~184%，并显著提升了土壤有机质（SOM）、阳离子交换量（CEC）及氮磷养分含量；而化肥处理对土壤重金属全量及有效态含量无显著影响，对土壤理化指标的提升相对较小。冗余分析（RDA）发现，猪粪组土壤全氮（TN）、CEC和速效磷（AP）分别解释了重金属方差变异的89.1%、6.4%和2.0%，化肥组土壤pH和全磷（TP）分别解释了方差变异的45.0%和22.2%，达到显著水平。进一步通过偏最小二乘路径模型（PLS-PM）分析发现，猪粪对重金属有效态的贡献远大于化肥，主要通过影响土壤重金属全量和CEC从而影响重金属有效性，其路径系数分别为0.621 7和0.295 3，均达到显著水平。猪粪组土壤重金属与理化指标之间由于“同源”关系呈显著正相关，而化肥组两者的关系受水稻生长活动等因素影响较大。研究表明，长期施肥可以通过调控土壤理化指标等影响重金属有效性，施用猪粪进行稻田土壤培肥的同时，需要注意土壤重金属的累积风险。

Effects of long-term application of pig manure and chemical fertilizers on soil Cu, Zn, and Cd contents and their availability in paddy soil

This study investigated the effects of long-term application of pig manure and chemical fertilizers on paddy soil in a field experiment that started in 1984. The total and available contents of soil copper(Cu), zinc(Zn), cadmium(Cd), soil physicochemical properties, grain yields, and their relationships were analyzed. The treatments included CK(control, no fertilizer), PK(chemical fertilizer P and K), NK(chemical fertilizer N and K), NP(chemical fertilizer N and P), NPK(chemical fertilizer N, P and K), and different proportions of pig manure plus chemical fertilizer(M1NPK, 30% manure + 70%NPK; M2NPK, 50% manure + 50%NPK; M3NPK, 70% manure + 30%NPK). The results showed that compared with CK, pig manure treatments significantly increased the total and available contents of Cu, Zn, and Cd by 134%~239%, 57%~124%, and 58%~171%, and 191%~380%, 285%~811%, and 61%~184%, respectively, and also significantly increased the soil organic matter(SOM), cation exchange capacity(CEC), total nitrogen(TN), total phosphorus(TP), alkali hydrolyzed nitrogen(AN), and available phosphorus(AP); however, the effects of chemical fertilizer treatments were not significant. Redundancy analysis(RDA)revealed that the soil TN, CEC, and AP accounted for 89.1%, 6.4%, and 2.0% of the variation in heavy metals, respectively, in pig manure treatments, whereas pH and TP accounted for 45.0% and 22.2% of the variance variation in heavy metals, respectively in chemical fertilizer treatments. Partial least squares path model(PLS-PM)analysis showed that the contribution of pig manure on the availability of heavy metals was much greater than that of chemical fertilizers. The availability of heavy metals was mainly affected by total heavy metals(THM)and CEC, and the path coefficients were 0.621 7 and 0.295 3, respectively. There was a significant positive correlation between heavy metals and soil physicochemical properties in pig manure treatments because of a homologous relationship, whereas the relationship among chemical fertilizer treatments was mainly affected by rice growth and harvest. This study indicated that when pig manure was used to improve soil fertility, long-term fertilization affected the availability of heavy metals by regulating soil physicochemical properties; hence, more attention should be paid to the risk of heavy metal accumulation in soils.