Southwick Lloyd M, Appelboom Timothy W, Fouss James L
Soil and Water Research, Agricultural Research Service, U.S. Department of Agriculture, 4115 Gourrier Avenue, Baton Rouge, Louisiana 70808, USA.
J Agric Food Chem. 2009 Feb 25;57(4):1413-20. doi: 10.1021/jf802468m.
The movement of the herbicide metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] via runoff and leaching from 0.21 ha plots planted to corn on Mississippi River alluvial soil (Commerce silt loam) was measured for a 6-year period, 1995-2000. The first three years received normal rainfall (30 year average); the second three years experienced reduced rainfall. The 4-month periods prior to application plus the following 4 months after application were characterized by 1039 +/- 148 mm of rainfall for 1995-1997 and by 674 +/- 108 mm for 1998-2000. During the normal rainfall years 216 +/- 150 mm of runoff occurred during the study seasons (4 months following herbicide application), accompanied by 76.9 +/- 38.9 mm of leachate. For the low-rainfall years these amounts were 16.2 +/- 18.2 mm of runoff (92% less than the normal years) and 45.1 +/- 25.5 mm of leachate (41% less than the normal seasons). Runoff of metolachlor during the normal-rainfall seasons was 4.5-6.1% of application, whereas leaching was 0.10-0.18%. For the below-normal periods, these losses were 0.07-0.37% of application in runoff and 0.22-0.27% in leachate. When averages over the three normal and the three less-than-normal seasons were taken, a 35% reduction in rainfall was characterized by a 97% reduction in runoff loss and a 71% increase in leachate loss of metolachlor on a percent of application basis. The data indicate an increase in preferential flow in the leaching movement of metolachlor from the surface soil layer during the reduced rainfall periods. Even with increased preferential flow through the soil during the below-average rainfall seasons, leachate loss (percent of application) of the herbicide remained below 0.3%. Compared to the average rainfall seasons of 1995-1997, the below-normal seasons of 1998-2000 were characterized by a 79% reduction in total runoff and leachate flow and by a 93% reduction in corresponding metolachlor movement via these routes. An added observation in the study was that neither runoff of rainfall nor runoff loss of metolachlor was influenced by the presence of subsurface drains, compared to the results from plots without such drains that were described in an earlier paper.
在1995年至2000年的6年期间，对密西西比河冲积土（商业粉质壤土）上种植玉米的0.21公顷地块中除草剂异丙甲草胺[2-氯-N-(2-乙基-6-甲基苯基)-N-(2-甲氧基-1-甲基乙基)乙酰胺]通过径流和淋溶的迁移情况进行了测量。前三年降雨量正常（30年平均值）；后三年降雨量减少。1995 - 1997年施药前4个月加上施药后接下来的4个月降雨量为1039±148毫米，1998 - 2000年为674±108毫米。在正常降雨年份，研究季节（除草剂施药后的4个月）径流为216±150毫米，同时伴有76.9±38.9毫米的渗滤液。在少雨年份，径流为16.2±18.2毫米（比正常年份少92%），渗滤液为45.1±25.5毫米（比正常季节少41%）。异丙甲草胺在正常降雨季节的径流为施用量的4.5 - 6.1%，而淋溶为0.10 - 0.18%。在降雨量低于正常水平的时期，这些损失在径流中为施用量的0.07 - 0.37%，在渗滤液中为0.22 - 0.27%。当对三个正常季节和三个降雨量低于正常水平的季节的平均值进行计算时，降雨量减少35%的情况下，异丙甲草胺的径流损失减少97%，以施用量的百分比计算，渗滤液损失增加71%。数据表明，在降雨减少时期，异丙甲草胺从表层土壤层淋溶迁移过程中的优先流增加。即使在降雨量低于平均水平的季节土壤中优先流增加，除草剂的渗滤液损失（占施用量的百分比）仍低于0.3%。与1995 - 1997年的平均降雨季节相比，1998 - 2000年降雨量低于正常水平的季节，总径流和渗滤液流量减少79%，通过这些途径的异丙甲草胺迁移减少93%。该研究中的另一个观察结果是，与早期一篇论文中描述的没有地下排水设施的地块的结果相比，降雨径流和异丙甲草胺的径流损失均不受地下排水设施的影响。
