USDA-ARS, Southeast Watershed Research Lab, P.O. Box 748, Tifton, Georgia 31793, USA.
J Agric Food Chem. 2009 Oct 28;57(20):9658-67. doi: 10.1021/jf9021527.
Pesticide use during crop production has the potential to adversely impact groundwater quality. In southern Florida, climatic and hydrogeologic conditions and agronomic practices indicate that contamination risks are high. In the current study, dissipation of the widely used herbicide, metolachlor, and levels of the compound and selected degradates in shallow groundwater beneath six 0.15-ha plots in sweet corn (Zea mays) production were evaluated over a two-year period. During fallow periods (May to October), plots were either left bare or cover cropped with sunn hemp (Crotalaria juncea L.). Metolachlor was broadcast applied at label recommended rates prior to planting sweet corn each year. Groundwater monitoring wells hydraulically upgradient and downgradient, and within each plot were sampled biweekly. Results showed that metolachlor dissipation was rapid, as evidenced by the detection of relatively high levels of the metolachlor ethane sulfonic degradate (MESA) in groundwater beneath plots and a rapid metolachlor DT(50) (9-14 days) in a companion laboratory soil incubation. Other degradates detected included hydroxymetolachlor in soil and in groundwater metolachlor oxanilic acid (MOA) and a product tentatively identified as 2-chloro-N-(2-acetyl-6-methylphenyl-N-(2-methoxy-1-methylethyl) acetamide, a photo-oxidation product. Metolachlor and MESA levels, up to 16 and 2.4 times higher in groundwater beneath the noncover cropped plots when compared to those of the cover cropped plots, indicate that cover cropping results in more rapid dissipation and/or reduced leaching. The study demonstrated that integration of cover crops into agronomic systems in the region may yield water quality benefits by reducing herbicide inputs to groundwater.
在作物生产过程中使用农药有可能对地下水质量造成不利影响。在佛罗里达州南部，气候和水文地质条件以及农业实践表明，污染风险很高。在当前的研究中，评估了在两年的时间里，在甜玉米（Zea mays）生产的六个 0.15 公顷的小块土地下，广泛使用的除草剂甲草胺的消解情况以及该化合物和选定降解物在浅层地下水中的水平。在休耕期（5 月至 10 月），土地要么裸露，要么种植黄麻（Crotalaria juncea L.）作为覆盖作物。每年在种植甜玉米之前，按照标签推荐的剂量撒播甲草胺。在每个地块的上、下游以及内部设置了地下水监测井，每两周采集一次水样。结果表明，甲草胺的消解速度很快，这从以下事实中可以看出：在地块下的地下水中检测到了相对较高水平的甲草胺乙磺酸降解物（MESA），以及在实验室土壤培养中快速消解甲草胺的 DT（50）（9-14 天）。在土壤和地下水中还检测到了其他降解物，包括羟基甲草胺、甲草胺氧苯胺（MOA）和一种暂定名为 2-氯-N-（2-乙酰基-6-甲基苯基-N-（2-甲氧基-1-甲基乙基）乙酰胺的光氧化产物。与覆盖作物种植的地块相比，未覆盖作物种植的地块下的甲草胺和 MESA 水平分别高出 16 倍和 2.4 倍，这表明覆盖作物种植可以促进甲草胺的快速消解和/或减少淋溶。该研究表明，在该地区将覆盖作物纳入农业系统可能会通过减少农药对地下水的输入，从而带来水质改善的好处。
