Water pressure head and temperature impact on isoxaflutole degradation in crop residues and loamy surface soil under conventional and conservation tillage management.
Laboratory incubations were performed in order to evaluate the dissipation of the proherbicide isoxaflutole in seedbed layer soil samples from conventional and conservation tillage systems and in maize and oat residues left at the soil surface under conservation tillage. The effects of temperature and water pressure head on radiolabelled isoxaflutole degradation were studied for each sample for 21d. Mineralisation of isoxaflutole was low for all samples and ranged from 0.0% to 0.9% of applied (14)C in soil samples and from 0.0% to 2.4% of applied (14)C in residue samples. In soil samples, degradation half-life of isoxaflutole ranged from 9 to 26h, with significantly higher values under conservation tillage. In residue samples, degradation half-life ranged from 3 to 31h, with significantly higher values in maize residues, despite a higher mineralisation and bound residue formation than in oat residues. Whatever the sample, most of the applied (14)C remained extractable during the experiment and, after 21d, less than 15% of applied (14)C were unextractable. This extractable fraction was composed of diketonitrile, benzoic acid derivative and several unidentified metabolites, with one of them accounting for more than 17% of applied (14)C. This study showed that tillage system design, including crop residues management, could help reducing the environmental impacts of isoxaflutole.
Université de Toulouse - École d'ingénieurs de Purpan, UMR 1248 AGIR INRA/INPT - 75, voie du TOEC BP 57 611, 31076 Toulouse cedex 3, France. lionel.alletto@purpan.fr
Lionel
L
Alletto
Yves
Y
Coquet
Valérie
V
Bergheaud
Pierre
P
Benoit
D003247:Conservation of Natural Resources / Q000379:methods*; D018556:Crops, Agricultural / Q000378:metabolism*; D007555:Isoxazoles / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008903:Minerals / Q000378:metabolism; D010573:Pesticide Residues / Q000737:chemistry / Q000378:metabolism; D011312:Pressure; D012987:Soil / Q000737:chemistry*; D013696:Temperature; D014867:Water
D007555:Isoxazoles; D008903:Minerals; D010573:Pesticide Residues; D012987:Soil; D014867:Water; C415327:isoxaflutole