Effect of Select Surfactants On Soil Biochemical Activity.

Surfactants are adjuvants used to formulate herbicides and insecticides to enhance adhesion to plant surfaces and increase efficiency.  Soils are one of the direct recipients of surfactants and little is known about the behavior and fate of these chemicals in soil ecosystems. In this study we used three surfactants: Activator, Agridex, and Thrust and  three herbicides: Gly-4, Atrazine, and Basagran. Treatments  included surfactant only, herbicide only and surfactant with herbicide combination. A greenhouse experiment was conducted using two different types of soils; silt loam and silty clay loam. Each pot (4000 g) was fertilized according to soil test recommendations. Pots were arranged in a randomized complete block design. Field corn was used as test crop and allowed to grow for seven weeks. Air dried soil samples from the greenhouse experimental pots  used for enzyme activity measurements. The acid phosphatase, b-glucosidase, b-glucosaminidase, arylsulfatase and dehydrogenase activities were determined. Phosphatase activity  measured using a method developed by Eivazi and Tabatabai (1977). Glucosidase, dehydrogenase and sulfatase determined using methods described by Tabatabai (1994) and b-glucosaminidase was assayed of Parham and Deng (2000). We hypothesized that treatments will alter soil microbial populations  and therefore, affecting enzyme activities in soils received  surfactant and/or herbicide or combination. In general, acid phosphatase activity was enhanced in this study by surfactant, Agridex, compared to control. Combination of  Agridex + Atrazine increased Phosphatase activity in silty clay loam soil. Combination of Agridex+ Atrazine and Thrust+Basagran increaed phosphatase enzyme activity in silt loam soil. Atrazine appeared to have the most inhibitory effect on enzyme activities in both silt loam and silty clay loam soils.