Degradation of a sulfonamide herbicide as a function of soil sorption

Abstract

Summary: Résumé: Zusammenfassung The degradation of DE‐498 (proposed common name flumetsulam) was studied in 21 US soils as a first step in developing a management plan for this new herbicide. Degradation half‐lives were shorter in soils that adsorbed the compound less. Adsorption was lower in soils with higher pH and lower organic carbon content. Degradation half‐lives were thus influenced by both pH and organic carbon: they were in the range 2–4 weeks in higher pH soils (pH 5 7.0) unless the organic carbon content was above 2.5%, at which half‐lives were in the range 1–3 months. In medium pH soils (6.4 pH 6.9) half‐lives were 1–2 months, while in lower pH soils (5.9 pH 6.3) they were 1–4 months. The laboratory data were supported by the response of sunflowers (Helianthus annuus L.) planted 1 year after application of flumetsulam to different soils. A quantitative model relating half‐life to sorption Kd (r2= 0.85) was coupled with an additional equation relating sorption Kd to the proportion of neutral and anionic forms of the compound at different pH values. The study allows estimates of this herbicide's degradation in soil to be made if its pH and organic carbon content are known. Degradation d'un herbicide sulfonamide en fonction de la capacité d'absorption du sol La dégradation du flumetsulam a étéétudiée dans les sols aux Etats Unis comme premier stade dans le développement d'un plan d'utilisation de ce nouvel herbicide. Les demi‐vies de dégradation étaient plus courtes dans les sols qui absorbaient moins le produit. L'absorption était plus faible dans les sols à pH élevé et à faible teneur en carbone organique. Les demi‐vies étaient ainsi sous l'influence du pH et du carbone organique: elles étaient de 2 à 4 semaines pour les pH de sols élevés (pH 7) sauf si le carbone organique était au dessus de 2,5%, dans ce cas, les demi‐vies etaient de 1 à 3 mois. Dans les sols à pH moyen (6,4 pH 6,9) les demi‐vies étaient de 1 à 2 mois, tandis que dans les sols à pH faible (5,9 pH 6,3) elles étaient de 1 à 4 mois. Les résultats de laboratoire ont été confirmés par le comportement de tournesols plantés un an aprfès l'application de flumetsulam dans différents sols. Un modèle reliant la demi‐vie au coefficient d'absorption Kd (r2= 0.85) a été couplé avec une équation additionelle reliant le coefficient d'absorption Kd à la proportion de particules neutres et anioniques de la molécule aux différents pH. L'étude permet de faire des estimations de la dégradation de cet herbicide dans le sol dès que le pH et la teneur en carbone organique sont connus. Abbau eines Sulfonamid‐Herbizids als Funktion der Bodensorption Der Abbau von Flumetsulam (DE‐498) wurde in 21 Böden untersucht, um eine Grundlage zur Produktentwicklung dieses neuen Herbizids zu gewinnen. Die 50%ige Verlustrate (DT50) war in schwächer sorptiven Böden kürzer. Bei hohem pH‐Wert und geringem Gehalt an organischer Substanz war die Adsorption schwächer. Die DT50 wurde durch den pH‐Wert und den Gehalt organischer Substanz wie folgt beeinflußt: Sie be...

Spatial Variability of Cyanazine Dissipation in Soil from a Conservation-Managed Field

“…The half-life of cyanazine was also positively correlated with sorption (Table II). Previous research supports evidence that herbicide sorption to soil contributes to protecting herbicide from degradation (16,29). Either an increase in clay or more acidic conditions would increase sorption and reduce cyanazine degradation, thereby supporting the correlations observed with sorption and half-life.…”

Yield and injury effects on vegetable crops planted in flumetsulam-treated soil

“…Flumetsulam adsorption to soil is highest at low soil pH (pH < 6.3) and high OM (>2.5%) (Lehmann et al 1992). Microbial degradation is the primary means of flumetsulam degradation in soils (Lehmann et al 1992;Rahman et al 1996) and high soil adsorption of flumetsulam reduces microbial availability (Shaw and Murphy 1997a). There is, therefore, increased flumetsulam persistence in soils with low pH and high OM.…”

“…Residues of flumetsulam can persist in the soil and injure sensitive crops grown in rotation with tolerant agronomic crops (Lehmann et al 1992). Soil residues as low as 0.01 to 0.07 ng g -1 can reduce growth of sensitive crops (Stork and Hannah 1996).…”

“…Soil residues as low as 0.01 to 0.07 ng g -1 can reduce growth of sensitive crops (Stork and Hannah 1996). The estimated half-life of flumetsulam in the soil ranges from 2 wk to 4 mo, depending on soil OM content and soil pH (Lehmann et al 1992). Soil OM and pH affect adsorption of flumetsulam and so are important factors governing its behaviour in soil (Fontaine et al 1991).…”

“…Soil OM and pH affect adsorption of flumetsulam and so are important factors governing its behaviour in soil (Fontaine et al 1991). Flumetsulam adsorption to soil is highest at low soil pH (pH < 6.3) and high OM (>2.5%) (Lehmann et al 1992). Microbial degradation is the primary means of flumetsulam degradation in soils (Lehmann et al 1992;Rahman et al 1996) and high soil adsorption of flumetsulam reduces microbial availability (Shaw and Murphy 1997a).…”