利用AAS研究农田土壤Cu,Zn和Cd含量及收支平衡

以沈阳生态实验站一组长期定位试验为平台，研究长期施用厩肥对农田土壤Cu，Zn和Cd含量及收支平衡的影响，试验处理分别为CK(不施有机肥)，M1(施10 t·ha-1有机肥)、M2(施用量25 t·ha-1) 和M3 (施用量50 t·ha-1)。结果表明：长期施用厩肥会造成土壤中Cu，Zn和Cd的逐步积累，且积累量随着施肥量的提高而增加，三种重金属在各处理中(CK，M1，M2，M3)的年均增长率分别为2.83%，6.56%，7.54%，8.96%;0.03%，3.44%，4.53%，6.64%和1.51%，8.01%，10.27%，16.08%。从试验开始6年后，M3处理土壤Cd含量已非常接近国家三级土壤质量标准的限制阈值(1 mg·kg-1，GB15618—1995);至试验第12年，所有施有机肥处理的土壤Cu含量均降为国家三级土壤质量标准(≤400 mg·kg-1)，因此必须给予足够的重视。尽管土壤中重金属呈逐年积累态势，但籽实中Cu，Zn和Cd含量均远低于国家食品污染标准(GB2762—2005; GB13106—91; GB15199—94)，表明重金属超标农田生产的农产品未必超标。Cu，Zn和Cd在作物秸秆中的含量远大于籽实中含量，不同处理作物重金属平均移出量表现为M3＞M2＞M1＞CK。CK，M1，M2，M3处理Cu，Zn和Cd的年均移出量分别为35.68，47.80，63.65，69.64;249.14，375.22，375.16，444.44和0.83，1.39，1.64，1.66 g·ha-1。有机肥中重金属含量也随年份而改变，表现为Cu和Zn含量逐年增加，Cd含量呈减少态势。M1，M2和M3处理土壤年平均残留Cu，Zn和Cd量为2 283.0，5 763.7，11 585.4;2 483.3，6 771.4，13 849.2和4.8，13.9，29.5 g·ha-1，但是由于有机肥中重金属量年际变化范围较大，年平均残留量只能反映多年的平均趋势，准确推断土壤中重金属残留量还要根据当年施入的有机肥的情况而定。

Study on Contents and Budgets of Cu,Zn and Cd in an Arable Soil Using AAS

Based on a long-term experiment in Shenyang Experimental Station, the effect of manure application on the contents and budgets of Cu, Zn and Cd in the arable soil was studied. The experiment included four treatments: no mature addition (CK), mature addition 10 t·ha-1 year-1 (M1), 25 t·ha-1 year-1 (M2), and 50 t·ha-1 year-1 (M3). The result showed that Cu, Zn and Cd in soil were accumulated with manure application and prolongation of experiment, and the accumulative magnitude increased with increasing of manure application. The average annual growth rates of the heavy metals in the four treatments (CK, M1, M2, M3) were 2.83%，6.56%，7.54%，8.96%;0.03%，3.44%，4.53%，6.64% and 1.51%，8.01%，10.27%，16.08% for Cu, Zn and Cd, respectively. After six years of the experiment, the content of Cd in the M3 treatment was quite close to the threshold of Chinese Soil Quality Standard Grade III (1 mg·kg-1, GB15618—1995). After 12 years of the experiment, the contents of Cu in the mature-amended treatments fell in the Chinese Soil Quality Standard Grade III, which should be paid more attention. Although the heavy metals in soil were gradually accumulated, the Cu, Zn and Cd levels in crop grain were still below the National Food Contamination Standards (GB2762—2005; GB13106—91; GB15199—94), indicating the contents of heavy metals in crop produced from contaminated soil might not exceed the corresponding standards. The contents of Cu, Zn and Cd in the straw were much greater than those in the grain. The removal of heavy metal by crop was in the order of M3>M2>M1> CK. The average amounts of Cu, Zn and Cd annually removed from the soil in the four treatments (CK, M1, M2 and M3) were 35.68, 47.80, 63.65, 69.64; 249.14, 375.22, 375.16, 444.44, and 0.83, 1.39, 1.64, 1.66 g·ha-1, respectively. The contents of heavy metals in organic manure varied in different years: the contents of Cu and Zn increased year by year, while Cd presented a decreasing trend. The average amounts of Cu, Zn and Cd annually remained in the soil in the treatments M1, M2 and M3 were 2 283.0, 5 763.7, 11 585.4; 2 483.3, 6 771.4, 13 849.2 and 4.8, 13.9, 29.5 g·ha-1, respectively. Since the heavy metals in organic manure markedly fluctuated in different years, the average residuals can only reflect the changing trend. Therefore, the residuals of heavy metals in the soil could be accurately predicted only according to status of manure in a given year.