Herbicide Reactivity of Soil Organic Matter Fractions in No‐Tilled and Tilled Cotton

Abstract

Because of the increased use of herbicides in no‐tilled soils and the difference in organic C distribution between tilled and no‐tilled soils, it is important to compare herbicide activity in different tillage systems. Soil humus fractions and characteristics were determined on surface Lexington silt loam soil (fine, silty, mixed, thermic Typic Paleudalf) samples of no‐tilled and tilled cotton field plots in West Tennessee. Soil humic and fulvic acid were extracted by standard methods. Total C ranged from 9.9 g kg−1 in the tilled soil to 13.5, 16.6 and 23.5 g kg−1 in the no‐tilled soils, with rye (Secale cereale L.), vetch (Vicia villosa Roth) and crimson clover (Trifolium incarnatum L.) cover crops, respectively. The tilled soil had the largest fraction of extractable C and fulvic acid, relative to total soil C. Humic acid was characterized by 13C‐NMR (nuclear magnetic resonance spectroscopy), titration of functional groups, and elemental analysis. Carboxyl groups determined by 13C‐NMR ranged from 6.1 to 7.7 mol kg−1 humic acid and compared more closely with total acidity than with carboxyl‐group determinations by titration. A greenhouse herbicide bioassay was conducted and sorghum [Sorghum bicolor (L.) Moench] growth was measured to indicate soil organic‐matter effects on the phytotoxicity of two herbicides. Herbicide activity was inversely related to soil C, extractable C, carboxyl groups of humic acid, and fulvic‐acid C. Fulvic‐acid C correlated best with herbicide activity. Decreased herbicide activity in tilled (no cover crop) soil was largely attributed to the C in tilled soil being in a more reactive state than C in no‐till (cover cropped) soil.

Tillage management effects on pesticide fate in soils. A review

“…However, to our current knowledge, little work has been published on the effects of these changes in soil organic matter composition due to tillage on pesticide sorption. Ding et al (2002b) highlighted a stronger sorption of metolachlor by humin than by humic acids, and humin content was found to be higher under notillage systems (Stearman et al, 1989). For humin, which is a highly condensed form of soil organic matter, several studies showed that sorption was more variable and that sorption isotherms were less linear (Xing and Pignatello, 1997;Yuan and Xing, 1999).…”

“…For humin, which is a highly condensed form of soil organic matter, several studies showed that sorption was more variable and that sorption isotherms were less linear (Xing and Pignatello, 1997;Yuan and Xing, 1999). In contrast, Stearman et al (1989) observed a higher sorption of metribuzin and oxyfluorfen on fulvic and humic acids, which are abundant in conventional tillage, than on humin, which is abundant in conservation tillage. Dissolved organic carbon content is most often higher under conservation tillage and is mainly composed of small molecules, with a size similar to that of fulvic acids (Suba and Essington, 1999).…”

Weed Population Dynamics

“…The pronounced reactivity of the OM is mainly related to its high specific surface area and presence of various functional groups such as carboxyl, hydroxyl and amine, and aliphatic and aromatic structures (STEVENSON, 1972;STEARMAN et al 1989;KUCKUK et al 1997). CHEFETZ et al (2004) observed greater adsorption of ametryn in sediment with 1.25 dag kg -1 of organic carbon in relation to the other with 1.63 dag kg -1.…”

Sorção do herbicida acetochlor em amostras de solo, ácidos húmicos e huminas de argissolo submetido à semeadura direta e ao preparo convencional

“…A MO apresenta acentuada capacidade de sorver herbicidas (Stevenson, 1972) e isto reduz a atividade biológica e a mobilidade dos compostos químicos aplicados ao solo (Lee & Farmer, 1989;Scheunert et al, 1992). A pronunciada reatividade da MO está relacionada principalmente com sua elevada área superficial específica e presença de vários grupos funcionais, como carboxilas, hidroxilas e aminas, e estruturas alifáticas e aromáticas (Stevenson, 1972;Stearman et al, 1989;Kuckuk et al, 1997).…”