Leaching of Imidazolinones in Irrigation Systems in Rice Cultivation: Sprinkling and Flooding

ABSTRACT: Herbicides of the imidazolinone group have been used in irrigated rice and presented a long persistence in the soil, especially in floodplain areas with a low drainage, and could cause environmental contamination. This study aims to evaluate the leaching and residual of herbicides belonging to the imidazolinone group in sprinkler and flood irrigation systems. The experiment was carried out under greenhouse conditions, with the application of the herbicides imazethapyr, imazethapyr + imazapic, and imazapyr + imazapic in soil irrigated by flooding and sprinkling. Subsequently, the soil was collected from the layers of 0-5, 5-10, 10-15, 15-20, and 20-25 cm and packed in 500 mL capacity plastic pots in order to sow tomato as a bioindicator plant of the presence of the herbicides belonging to the imidazolinones. Phytotoxicity, length, and shoot dry matter mass of tomato plants were evaluated at 10 and 20 days after emergence. The herbicides of the imidazolinone chemical group presented a high potential for leaching and persistence with effects for more than 180 days after application. Based on the symptoms presented by the sensitive crop, the degradation of imazethapyr, imazethapyr + imazapic, and imazapyr + imazapic in the 0-15 cm layers was higher in soil with sprinkler irrigation when compared to flood irrigation. Thus, non-flooded soils present a greater capacity to degrade the herbicides belonging to the imidazolinone chemical group.

摘要：咪唑啉酮类除草剂（imidazolinone group）已被用于灌溉稻田种植，且在土壤中持效期较长，尤其在排水不良的泛滥平原区域，易造成环境污染。本研究旨在评估咪唑啉酮类除草剂在喷灌与漫灌系统中的淋溶特性与残留行为。试验于温室条件下开展，分别在漫灌和喷灌的土壤中施用咪唑乙烟酸（imazethapyr）、咪唑乙烟酸+咪唑喹啉酸（imazethapyr + imazapic）以及咪唑烟酸+咪唑喹啉酸（imazapyr + imazapic）。随后采集0-5、5-10、10-15、15-20、20-25 cm土层的土壤，装入500 mL容量的塑料盆中，用于播种番茄，以作为检测咪唑啉酮类除草剂残留的生物指示植物。在番茄出苗后10天和20天，分别测定其药害（phytotoxicity）、株高及地上部干物质质量。研究结果表明，咪唑啉酮类化学除草剂具备较强的淋溶与残留潜力，施药后180天仍可产生生物效应。基于敏感作物的受害症状，与漫灌土壤相比，喷灌土壤0-15 cm土层中的咪唑乙烟酸、咪唑乙烟酸+咪唑喹啉酸以及咪唑烟酸+咪唑喹啉酸的降解程度更高。由此可见，非漫灌土壤对咪唑啉酮类化学除草剂的降解能力更强。