|Banks, Mona-lisa - University Of Missouri|
|Eivazi, Freida - Lincoln University Of Missouri|
|Motavalli, Peter - University Of Missouri|
|Nelson, Kelly - University Of Missouri|
Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2012
Publication Date: N/A
Interpretive Summary: Agricultural pesticides are generally combined with other chemical agents resulting in the formulated products that are commercially available for use on field crops. The additional chemicals are necessary to improve the effectiveness of the active pesticide compound in suppressing or killing the target pest. For herbicides, important formulation ingredients include surfactants, which increase wettability and spreadability, enhance toxicity, and increase penetration of the herbicide chemical into the leaves of weeds. Effects of herbicide active ingredients on soil function and plant growth have received the greatest attention from researchers; however, even though surfactants are applied coincidentally with herbicides, little research on similar effects of these chemicals has been conducted. Our research objective was to examine potential effects of surfactants, with or without herbicides, on nutrient uptake by corn grown in two different soils, a silt loam and a silty clay loam. We evaluated three commonly used surfactants, Activator-90, Agri-Dex, and Thrust that are used with the herbicides glyphosate, atrazine, and bentazon, respectively. The surfactants and respective herbicide combinations were applied to the soils in the greenhouse before planting with corn. Corn was allowed to grow until the eight-leaf stage (or seven weeks after emergence) when the plants were harvested and analyzed for nutrient contents. A few treatments altered nutrient uptake by corn after a single application. Soil texture appears to be a factor that influenced the effect of surfactant on nutrient uptake in corn. For example, potassium was the only nutrient with uptake decreased by one surfactant (Thrust) in the silt loam whereas uptake of six nutrients was negatively affected in the silty clay loam by either the surfactants Activator-90 and Thrust, or all surfactant-herbicide combinations. Actual decreases in nutrient uptake ranged from 10 to 30% relative to non-treated controls and did not affect vegetative production since biomass accumulation did not differ for any treatment. This study should be repeated in the field to verify the effects of surfactants under natural conditions and if a potential for grain yield decreases exist. However, the results are important to agronomists, extension personnel, farmers, and agricultural chemical representatives because the results show that herbicide formulation chemicals may potentially affect nutrient uptake by corn differently depending on the soil on which the crop is grown. Information on effects of surfactants on plant nutrition may be useful in considering potential impact of such chemicals when developing fertility and weed management strategies for specific soils.
Technical Abstract: Surfactants with solvent and wetting abilities are used in the formulation of herbicides to enhance spraying capabilities. These chemicals eventually enter into the soil and may disrupt different chemical, physical and biological processes. The aim of this study was to examine the effects on nutrient uptake in corn due to application of surfactants at different rates, herbicides, and surfactant-herbicide combinations in silt loam and silty clay loam soils. Surfactants used at field application rates were Activator 90, Agri-Dex and Thrust. Herbicides used were glyphosate, atrazine, and bentazon. Corn was planted in fertilized soils and moisture levels maintained for optimum growth. At seven weeks (V8 growth stage), plant foliage was collected, dried, and ground for elemental analyses. In general, treatments differentially affected plant nutrient uptake, primarily due to differences in soil texture. Potassium uptake was significantly (P=0.05) decreased in silt loam by Thrust but uptake of P, K, Ca, S, Cu, and Zn were decreased by up to 30 percent when surfactants and/or surfactant-herbicide combinations were applied to silty clay loam. Surfactants as a formulation additive may contribute to effects of pesticides on plant nutrient uptake depending on certain soil properties including texture as demonstrated in this study. Further long-term field studies are needed to determine changes in nutrient uptake and potential impact on grain yield after several years of annual applications of surfactants plus herbicides.