Isoproturon Sorption and Degradation in a Soil from Grassed Buffer Strip
1999
Benoit, P. | Barriuso, E. | Vidon, Ph | Réal, B.
The fate of the herbicide isoproturon [3-(4-isopropylphenyl)-l,1-dimethylurea] was investigated in soil from a grassed buffer strip. Compared to a cropped soil originating from the same experimental site (Kd = 1.8 L kg⁻¹), sorption of isoproturon was enhanced in the grassed soil and especially in the surface layer (0-2 cm) containing high proportion of nondecomposed plant residues (Kd = 5.0 L kg⁻¹). Nonhumified organic fractions isolated from the surface soil layer and corresponding to above and bdow-ground plant residues derived from the grass exhibited high sorption coefficients Kd and Kₒc compared to the rest of the soil. Reversibility of sorption was lower in the grassed soil than in the cropped soil and decreased rapidly with time. A rapid degradation of isoproturon was observed at different depths of the grassed soil whereas most of the herbicide remained nondegraded in the cultivated soil: half-lives were respectively 72 d in the cultivated soil, and only 8 d in the superficial layer (0–2 cm) of the grassed soil. The highest mineralization rate of the isoproturon ring (20% after 35 d) was observed in the top layer (0–2 cm) having the highest mineralization rates of organic matter. In relation with this fast degradation, a large proportion of isoproturon residues became nonavailable to water and methanol extractions (54% of the initial applied isoproturon found as nonextractable (bound) residues). Thus the grassed strip surface soil had a high potential to dissipate isoproturon trapped from run-off.
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