长期不同施肥塿土对外源Cr(Ⅲ)形态转化的影响

Transformations of Fractions of Exogenous Chromium(Ⅲ)in Manural Loess Soil After Long-term Fertilization

以23年长期不同施肥处理（不施肥CK，施氮磷钾化肥NPK，有机肥配合化肥MNPK）土壤为材料，外源添加浓度为500 mg·kg-1 Cr，经过90 d的室内培养，研究了土壤pH、有效态Cr及各个形态Cr含量随培养时间的变化。结果表明：外源添加Cr导致土壤pH下降了0.4~0.6个单位；施肥显著降低了土壤有效Cr含量，在培养结束后，NPK处理土壤有效态Cr较CK下降了约34％， MNPK处理土壤有效态Cr的含量几乎为零。长期施用NPK处理土壤铁锰氧化物结合态Cr和有机结合态Cr含量分别较CK提高了12％和38％，而可交换态Cr含量却较CK下降了约27％，但碳酸盐结合态和残渣态Cr含量与CK相比无显著差异；长期施用MNPK土壤可交换态、碳酸盐结合态、铁锰氧化物结合态Cr含量分别较NPK处理降低了100％、44％和29％,而有机结合态和残渣态Cr含量却分别提高了72％和17％。研究表明长期合理施肥，尤其是化肥配合有机肥施用可以显著提高塿土恢复力，降低塿土重金属Cr污染的危害。

Fractions and bioavailability of heavy metals in soils varied among different soils, thus impacting soil resilience to heavy metal contamination. We spiked two levels of Cr（Ⅲ）（0 and 500 mg·kg-1）to soils subjected to different fertilization for 23 years and incubated the soils for three months. The fertilizer treatments included（1）no fertilizer（CK）,（2）mineral nitrogen, phosphate and potassium（NPK）, and（3）organic manure integrated with NPK（MNPK）. Soil Cr fractions were measured with sequential extraction. Spiking Cr decreased soil pH by 0.4 to 0.6 units. Long-term fertilization significantly reduced bioavailability of exogenous Cr. Compared with no fertilizer（CK）, soil bioavailable Cr was 34% lower in NPK and almost 100% lower in MNPK. In NPK soil, iron and manganese oxides bounded and organic bounded fractions increased by 12%and 38%, respectively;exchangeable Cr contents decreased by 27%;no significant changes were ob-served in carbonates bounded and residual Cr fractions, as compared with the CK. In MNPK soil, contents of exchangeable, carbonates bounded, iron and manganese oxides bonded Cr were 100%, 44%and 29%lower;whereas organic bounded and residual Cr were 72%and 17%higher than in NPK, respectively. These results suggest that long-term organic-inorganic fertilizer management can significantly im-prove the resilience of loess soil and thus alleviate the impairment of chromium contamination.