Cultivation affects pesticide–soil interactions

Pesticides are often used to enhance crop production by killing unwanted animals or plants. Unfortunately, they can also negatively impact humans and environmental health. The degree of impact, in part, depends on the fate and behavior of pesticides in the environment. The latter is governed by complex interactions of pesticides with soil components.

One such important interaction is sorption of pesticides on soil. A new study in the November–December 2009 issue of the Soil Science Society of America Journal demonstrates that the mechanism and capacity of pesticide sorption on soil were affected by the nature and quantity of soil organic carbon, which were altered by land use and cultivation.

A research team at Oklahoma State University investigated the nature of soil organic carbon, chemical composition, and sorption behavior of a non-ionic organophosphate pesticide, phosalone, in 21 soils with a wide range of soil properties and land uses. The nature of soil organic carbon was evaluated based on the relative proportions of different chemical functional groups in organic carbon as revealed by solid-state nuclear magnetic resonance.

Despite a widely varied cultivation history and input of organic materials such as wheat, corn, cotton, grasses, and tree residues, intrinsic basic soil properties and climate region played a predominant role in dictating the nature of soil organic matter. When comparing cultivated and uncultivated soils, composition and quantity of soil organic carbon are markedly different.

The relative proportions of aromatic organic compounds were higher, and aliphatic organic compounds were lower in cultivated soils than the uncultivated soils, with the aromaticity of cultivated soils being 1.3 times that of uncultivated soils. Differences in soil organic carbon composition and quantity led to differences in the sorption behavior of phosalone in soil, with stronger sorption to uncultivated soils than cultivated soils. Pesticide binding strength was correlated with organic carbon content in uncultivated soils but not in the cultivated soils, suggesting distinctly different mechanisms of phosalone sorption in soils with or without cultivation.

The authors say this study provides valuable information for environmental protection. Understanding the factors affecting partitioning of a pesticide in soil would help researchers determine the potential of a pesticide to leach into the groundwater, persist, or biodegrade following the release into the soil environment. They say the study also demonstrates that cultivation history needs to be considered when developing a pesticide management plan for sustainable agricultural production.

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