Oxyfluorfen bioavailability in Brazilian Savanna soils

ABSTRACT Oxyfluorfen is a pre-emergent herbicide applied via soil; however, the soil attributes have not been considered to predict the herbicide doses. This study aimed to evaluate the bioavailability of the oxyfluorfen herbicide in Brazilian Savanna soils with contrasting attributes. The experiment was carried out in a 6 x 8 factorial scheme, with 6 replications. The evaluated factors were soil types [Gleissolo Melânico distrófico - GMd (Typic Humaquept); Latossolo Vermelho ácrico - LVw (Rhodic Acrustox); Latossolo Vermelho distrófico - LVd (Rhodic Haplustox); Neossolo Quartzarênico órtico - RQo (Typic Quartzpsamment); Neossolo Flúvico Tb distrófico - RYbd (Fluventic Dystrustept); and washed sand] and oxyfluorfen doses (0; 360; 480; 720; 1,440; 2,880; 4,320; and 5,760 g a.i. ha-1). The herbicide bioavailability was determined according to the bioassay methodology. The dose that provided 80 % of Cucumis sativum control (C80%) ranged from 9.9 (LVw) to 1,884.4 g a.i. ha-1 (GMd), what can be attributed to the high sorption of the herbicide in the GMd, as observed by the adsorptive rate. The soil texture did not show correlation with the oxyfluorfen bioavailability. In the LVd, which is from the same order and with texture similar to that of the LVw, the C80% was 76 times higher (754.28 g a.i. ha-1). Furthermore, for the RYbd, which is a sandy soil, the C80% was even high (1,256.9 g a.i. ha-1). The cation exchange capacity (CEC) (-0.83**) was the only soil attribute able to predict the herbicide bioavailability. The oxyfluorfen bioavailability is highly dependent on the soil attributes, and, in Brazilian Savanna soils, it can be predicted using the CEC.

摘要：乙氧氟草醚（Oxyfluorfen）是一种通过土壤施用的苗前除草剂（pre-emergent herbicide），但目前尚未结合土壤属性开展该除草剂施用剂量的预测研究。本研究旨在评估不同土壤属性的巴西塞拉多（Brazilian Savanna）土壤中乙氧氟草醚的生物有效性。实验采用6×8因子设计，设置6次重复。试验因子包含两类：其一为土壤类型[腐殖质不饱和潜育土（Gleissolo Melânico distrófico，GMd，对应Typic Humaquept）、酸性红色铁铝土（Latossolo Vermelho ácrico，LVw，对应Rhodic Acrustox）、不饱和红色铁铝土（Latossolo Vermelho distrófico，LVd，对应Rhodic Haplustox）、钙质石英质新成土（Neossolo Quartzarênico órtico，RQo，对应Typic Quartzpsamment）、不饱和层状冲积新成土（Neossolo Flúvico Tb distrófico，RYbd，对应Fluventic Dystrustept）以及水洗砂]；其二为乙氧氟草醚施用剂量（0、360、480、720、1440、2880、4320和5760 g a.i. ha⁻¹）。采用生物测定法（bioassay methodology）确定该除草剂的生物有效性。使黄瓜（Cucumis sativum）防治效果达到80%的施用量（C80%）范围为9.9（LVw）至1884.4 g a.i. ha⁻¹（GMd），这一结果可归因于乙氧氟草醚在GMd土壤中的高吸附性，吸附速率的测定结果也证实了这一点。土壤质地（soil texture）与乙氧氟草醚的生物有效性未呈现相关性。对于同属一级分类且质地与LVw相近的LVd土壤，其C80%高达754.28 g a.i. ha⁻¹，为LVw的76倍。此外，作为砂质土壤的RYbd，其C80%同样处于较高水平（1256.9 g a.i. ha⁻¹）。阳离子交换量（cation exchange capacity, CEC）（相关系数为-0.83**）是唯一可用于预测该除草剂生物有效性的土壤属性。综上，乙氧氟草醚的生物有效性高度依赖土壤属性，在巴西塞拉多土壤中，可通过阳离子交换量对其进行预测。