Field dissipation of acetochlor in two New Zealand soils at two application rates

• Published in: Journal of environmental quality Vol. 33; no. 3; pp. 930 - 938
• Main Authors: Ma, Q, Rahman, A, Holland, P.T, James, T.K, McNaughton, D.E
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01.05.2004; Crop Science Society of America; American Society of Agronomy
• Subjects: Acetochlor; Agronomy. Soil science and plant productions; application rate; Applied sciences; Biological and medical sciences; Clay loam; clay loam soils; degradation; duration; Earth sciences; Earth, ocean, space; Energy dissipation; Engineering and environment geology. Geothermics; Environmental impact; Environmental Monitoring; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Herbicides - analysis; High temperature; Kinetics; mathematical models; Models, Theoretical; New Zealand; Organic carbon; pesticide application; pesticide persistence; Pesticides; Photolysis; Pollution; Pollution, environment geology; Risk assessment; Sandy loam; sandy loam soils; Sandy soils; Soil; Soil Pollutants - analysis; Soil Pollutants - metabolism; soil pollution; Soil surfaces; Soils; Temperature; Toluidines - analysis; New Zealand; Oceania; Concentration measurement; Persistence; Kinetic model; Photolysis; Pollutant behavior; Risk assessment; Pesticides; Kinetics; Modeling; Clay loam soil; Sandy loam soil; Photochemical degradation
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2004.0930

The persistence of pesticides in soils has both economic and environmental significance and is often used as a key parameter in pesticide risk assessment. Persistence of acetochlor [2'-ethyl-6'-methyl-N-(ethoxymethyl)-2-chloroacetylanilide] in two New Zealand field soils was measured over two years and the data were used to identify models that adequately describe acetochlor persistence in the field. Acetochlor was sprayed onto six fallow plots (3 x 9 m each) at each site at the recommended rate (2.5 kg a.i. ha(-1)) and at twice that rate. Acetochlor concentrations were measured in soil cores. Simple first-order kinetics (Model 1) adequately described acetochlor persistence in Hamilton clay loam soil (Humic Hapludull, Illuvial Spadic) at the high application rate, but overestimated it at the low application rate. A quadratic model (Model 2), a first-order double-exponential model (Model 3), a first-order biphasic model (Model 4), or a two-compartment model (Model 5) better described acetochlor persistence at the low application rate. The time for 50% (DT50) and 90% (DT90) of initial acetochlor loss was approximately 9 and 56 d, and 18 and 63 d at low and high application rates, respectively. The more complex Models 2 through 5 also better described the biphasic dissipation of acetochlor in Horotiu sandy loam soil (Typic Orthic Allophanic) than Model 1, with Model 1 significantly underestimating acetochlor concentrations on the day of application at both application rates. The DT50 and DT90 values were 5 and 29 d and 7 and 31 d at low and high application rates, respectively. Overall, application rate significantly affected the DT50 and DT90 values in the Hamilton soil, but not in the Horotiu soil. Faster acetochlor loss in the Horotiu soil possibly resulted from the higher soil organic carbon content that retained more acetochlor near the soil surface where higher temperature and photolysis accelerated the loss.