Adsorption and degradation of triazine herbicides in soils used for lupin production in Western Australia: Laboratory studies and a simulation model

Walker, S. R. and Blacklow, W. M. (1994) Adsorption and degradation of triazine herbicides in soils used for lupin production in Western Australia: Laboratory studies and a simulation model. Australian Journal of Soil Research, 32 6: 1189-1205.


Author Walker, S. R.
Blacklow, W. M.
Title Adsorption and degradation of triazine herbicides in soils used for lupin production in Western Australia: Laboratory studies and a simulation model
Journal name Australian Journal of Soil Research   Check publisher's open access policy
Publication date 1994
Sub-type Article
DOI 10.1071/SR9941189c
Volume number 32
Issue number 6
ISSN 0004-9573
Start page 1189
End page 1205
Total pages 17
Place of publication Collingwood, Vic., Australia
Publisher CSIRO Publishing
Language eng
Abstract Most lupins (Lupinus angustifolius L. and L. albus L.) grown in Western Australia are sown with simazine, and some with atrazine, to give persistent control of a broad spectrum of weeds. Rates of application are adjusted for soil types yet there can be ineffective weed control and crop damage. The kinetics of degradation in four soils was studied in the laboratory to determine how it varied between soils and was modified by soil temperature, pH, moisture and gamma irradiation. The time for half the herbicide to be lost from the soils (HL) varied from 42 to 110 days at 20°C and -0.08 MPa water potential. Loss was rapid in the first day of incubation and subsequent losses were described precisely by first-order functions. However, the first-order half-lives (t1/2) were 3-21 days greater than the corresponding HLs, because the first-day losses were unaccounted for by the first-order functions. Gamma irradiation had no influence on degradation kinetics which supported chemical hydrolysis as the mechanism of degradation. The t1/2 values were correlated positively with the proportion of applied herbicide that was adsorbed by the soils (PAd). Atrazine was more persistent than simazine and had higher PAd values. The PAd values increased with soil pH, organic matter and clay content. The t1/2 values decreased exponentially with temperatures from 28 to 9-degrees-C, and decreased with soil water potentials from -0.08 to -1.50 MPa for a loamy sand at a near-neutral pH. A computer simulation model gave good agreement with observed residue decays and showed that the initially rapid losses from the soils could be explained by high rates of hydrolysis when all the applied herbicide was in the soil solution and, consequently, herbicide concentrations were high (87-100 mM). Rapid losses of the triazines in the field are likely in warm, acidic soils-particularly if the herbicide concentrations in the soil solution are high for reasons of limited vertical distribution of the applied herbicides through the soil profile.
Keyword Simazine
Atrazine
Chemical Hydrolysis
Reaction Kinetics
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ
Additional Notes Journal title since 2011: Soil Research (1838-675X; 1838-6768)

Document type: Journal Article
Sub-type: Article
Collection: Queensland Alliance for Agriculture and Food Innovation
 
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