Clomazone Leaching Estimate in Soil Columns Using the Biological Method

ABSTRACT The chemical control of weed is a necessary practice in large-scale agriculture. However, when herbicides are used in the wrong way, they can remain into soil for long periods and/or be leached in its profile, and they may even contaminate groundwater. In this research, clomazone leaching in soil samples collected from different Brazilian regions was estimated by biological method. To do so, columns containing soils were used, and samples were collected every 5 cm. After preparing columns and applying a 1,500 g a.i. ha-1 clomazone dose, rain simulation was performed. Sorghum was used in order to detect the herbicide. More than 60% similarity was found for the studied variables; it was chosen to use only data referring to toxicity percentage. Clomazone did not cause reduction in sorghum cultivated in Organosol, thus indicating a strong herbicide sorption in this soil. Increased pH in Oxisol reduced leaching. More rainfall caused increased herbicide leaching in Oxisol (pH 5.1) and Quartzarenic Neosol. The highest leaching occurred in soils with lower pH and lower organic matter content. It is possible to conclude that, in soils with higher organic matter content, clomazone has lower risks of being leached.摘要 化学除草是规模化农业生产中不可或缺的作业环节。然而，除草剂使用不当会长期残留于土壤中，或随土壤剖面淋失，甚至污染地下水。本研究通过生物学方法评估了巴西不同地区采集的土壤样品中异恶草酮（clomazone）的淋溶情况。实验采用土壤柱装置，每5 cm分层采集样品。在完成柱体装填与1500克有效成分/公顷的异恶草酮施用量处理后，开展模拟降雨试验。以高粱作为指示作物检测除草剂残留。经分析，所研究的各变量间相似度超过60%，因此最终仅选取与毒性百分比相关的数据开展后续分析。异恶草酮对种植于有机土（Organosol）中的高粱未产生生长抑制作用，表明该土壤对该除草剂具有较强的吸附能力。氧化土（Oxisol）的pH升高可降低除草剂淋溶风险。降雨量增加会提升pH为5.1的氧化土与石英砂质新成土（Quartzarenic Neosol）中的除草剂淋溶量。淋溶程度最高的样本均来自低pH、低有机质含量的土壤。综上可得出结论：有机质含量更高的土壤中，异恶草酮发生淋溶的风险更低。