Sorption of clopyralid, dicamba and MCPA by two soils with conventional and no-till management

Abstract

Shang, C. and Arshad, M. A. 1998. Sorption of clopyralid, dicamba and MCPA by two soils with conventional and no-till management. Can. J. Soil Sci. 78: 181-186. Sorption is one of the key processes controlling the fate of agrochemicals in soil systems. The sorption of agrochemicals on a soil matrix can be affected by changes in chemical and physical properties caused by different tillage practices. Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), dicamba (3,6-dichloro-2-methoxybenzoic acid), and MCPA ((4-chloro-2-methylphenoxy)acetic acid), weakly acidic herbicides, are commonly used to control broadleaf weeds in crop production. The sorption of the three herbicides by surface soils (0-5 cm) from different tillage systems was studied by batch equilibrium. Of the herbicides used, MCPA was sorbed on soil in the greatest quantity, dicamba was the least sorbed, and the sorp-tion was dependent on the pK a values of herbicides. In a sandy loam soil, more herbicide was sorbed under no-tillage (NT) than conventional tillage (CT). However, in a clay soil the difference in herbicide sorption between the two tillage systems was not consistent. The results can be explained in terms of changes in soil pH and organic matter content. The presence of clopyralid and MCPA lowered the sorption of dicamba, and MCPA was more effective than clopyralid in competing for sorption sites with dicamba. Shang, C. and Arshad, M. A. 1998. Sorption du clopyralide, du dicamba et du MCPA sur deux sols exposés au travail classique ou à la culture sans travail du sol. Can. J. Soil Sci. 78: 181-186. La sorption est l'un des mécanismes clés déterminant le devenir des produits agrochimiques dans le sol. La sorption de ces produits sur la matrice du sol peut varier selon les modifications des propriétés chimiques et physiques du sol résultant des différentes pratiques culturales utilisées. Le clopyralide (acide dichloro-2, 3 pyrine-2 carboxylique), le dicamba (acide dichloro-3,6 méthoxy-2 benzoïque) et le MCPA (acide chloro-4 méthyl-2 phénoxy-acétique), herbicides de faible acidité sont couramment utilisés pour la lutte contre les dicotylédones dans les cultures. Nous avons examiné par la méthode d'équilibration fractionnée la sorption des 3 substances dans le sol de surface (0-5 cm) résultant de divers systèmes de travail du sol. C'est le MCPA qui était adsorbé en plus forte quantité et le dicamba en plus faible quantité et le taux de sorption dépendait des valeurs pK a de l'herbicide. En loam sableux, la sorption était plus importante en régime de culture sans labour qu'en régime de travail classique. En sol argileux, les différences observées selon les 2 régimes de travail du sol n'étaient pas régulières. Les résultats s'expliquaient par les modifications du pH et de la teneur en matière organique du sol. En présence de clopyralide et de MCPA, la sorption du dicamba était moins forte, le MCPA s'avérant, par ailleurs, plus efficace que le clopy-ralide pour disputer au dicamba les sites de sorption.

Sorption of Bentazone, Dichlorprop, MCPA, and Propiconazole in Reference Soils from Norway

“…It may be difficult to compare results if K F values are derived from different units of C s and C w or if C w ≤1 or if 1/ n values differ (Chen et al, 1999). However, the results are roughly within the range of previously reported values (Grey et al, 1996; Gaston et al, 1996; Matallo et al, 1998; Riise and Salbu, 1992; Ghorayshi and Bergström, 1991; Helweg, 1987; Susarla et al, 1992; Riise et al, 1994, Shang and Arshad, 1997; Socías‐Viciana et al, 1999; Liu and Weber, 1986). Higher K F values for all pesticides were found in soil from Froland with a high organic content and a low pH, which is consistent with previously mentioned literature that also reports higher increasing K F in soil with increasing organic content.…”

Modeling Macropore Flow Effects on Pesticide Leaching

“…The estimated k oc values varied between 35 and 147 cm 3 g −1 , with an average of 89 cm 3 g −1 , which is within the range of values reported for MCPA in the literature (Helweg, 1987; Riise et al, 1994; Shang and Arshad, 1998; Socías‐Viciana et al, 1999). Encouragingly, the degradation rate coefficient seemed to be well identified by the procedure, with the smallest coefficient of uncertainty of all estimated parameters (mean of 6.6%).…”

“…As expected, the organic‐rich hollow column had a sorption coefficient approximately 12 and 2 times larger than the hilltop and slope columns, respectively (Table 7). Adsorption of the weak acid MCPA is affected by soil pH (Riise et al, 1994; Shang and Arshad, 1998). However, since the variation in soil pH was small (Table 1) and pH was much higher than the compound pK a (3.07; Nicholls, 1994), this effect was ignored and effective k oc values were estimated from the calibrated sorption coefficient k d and the organic carbon content f oc in the columns, following the relation: …”

Dissipation of the Herbicide Clopyralid in an Allophanic Soil: Laboratory and Field Studies

“…It is likely that under shaded conditions, a portion of the herbicide was closely associated with the soil organic matter and soil water contents were sub-optimal for microbial activity. [25] Another process that may partly explain the above results could be the sorption of clopyralid to clay minerals of the soil matrix [26] being more important at low water contents. Rahman et al [8] found a significant correlation (r = À 0.56) between clopyralid persistence and clay content.…”