Leaching and Persistence of Sulfentrazone when Mixed with Adjuvants

ABSTRACT: The objective of this work was to study the influence of adjuvants on leaching and persistence of sulfentrazone in a Red-Yellow Ultisol. The soil was stored in PVC columns of 10 cm diameter and 50 cm length. The treatments were composed of sulfentrazone mixed with six adjuvants (Adesil®, Break-Thru®, Assist®, Hoefix®, Fera® and Nortox® Vegetable Oil), a treatment with sulfentrazone without any adjuvant and a treatment without the herbicide. In the treatments with sulfentrazone, the herbicide was applied at a rate of 1.0 kg ha-1 at the top of the columns, and 12 hours after application, the columns were subjected to simulated rainfall (60 mm). To confirm leaching of sulfentrazone, soil samples were collected every 5 cm up to 50 cm in each column and transferred to 300 cm3 pots to conduct a bioassay using the species Sorghum bicolor. At 21 days after emergence (DAE) of sorghum, visual assessment of intoxication was performed and shoot dry matter percentage was determined. To determine the influence of adjuvants on persistence of sulfentrazone in the soil, new sorghum seeds were planted as soon as the sorghum plants from the first planting were cut; also, phytotoxicity scores were assigned and shoot dry matter was determined at 21 DAE. This procedure was repeated up to 173 days after herbicide application, when the plants showed no more visual symptoms of intoxication. The adjuvant Break-Thru® was effective at reducing leaching of sulfentrazone. The presence of adjuvants applied together with sulfentrazone did not influence the persistence of the herbicide in the study soil. Persistence of sulfentrazone lasted for 143 days.摘要：本研究旨在探究助剂对红黄色老成土（Red-Yellow Ultisol）中磺草唑胺（sulfentrazone）淋溶特性与土壤持留性的影响。试验将供试土壤装填于直径10 cm、长度50 cm的PVC柱体中。试验处理共设三类：一是磺草唑胺与6种助剂（Adesil®、Break-Thru®、Assist®、Hoefix®、Fera®及Nortox®植物油）复配的处理组；二是仅施用磺草唑胺的无助剂对照组；三是不施加除草剂的空白对照组。在含磺草唑胺的处理组中，除草剂施用量为1.0 kg·ha⁻¹，施用于柱体顶部；施药12小时后，对柱体施加60 mm的模拟降雨。为验证磺草唑胺的土壤淋溶情况，每5 cm采集一层土壤样品直至50 cm深度，将采集的土壤样品转移至300 cm³的盆钵中，采用高粱（Sorghum bicolor）开展生物测定。在高粱出苗后21天（Days After Emergence，DAE），对植株的药害症状进行目视评估，并测定地上部干物质百分率。为明确助剂对磺草唑胺土壤持留性的影响，在首次种植的高粱植株收割后立即重新播种高粱种子，同样于出苗后21天开展药害评分与地上部干物质测定。上述实验流程重复进行，直至施药后173天，此时供试植株无可见药害症状。试验结果显示：助剂Break-Thru®可有效降低磺草唑胺的土壤淋溶；与磺草唑胺配合施用的助剂对供试土壤中该除草剂的持留性无显著影响；磺草唑胺在供试土壤中的持留时长为143天。