Submitted to: Environmental Contamination and Toxicology Bulletin
Publication Type: Other
Publication Acceptance Date: 5/22/1995
Publication Date: N/A
Interpretive Summary: Conventional production of corn relies on intensive use of pesticides to control insects and weeds that can devastate grain yield and quality. Application of pesticides to production fields might also impact water quality if the chemicals move over or through soil into water before they are degraded in the soil. Most studies of pesticide fate in the environment consider the whole field condition to describe potential degradation. We examined individual parts of the system, the soil and the plant, to see what the impact of plants and the microorganisms associated with plant roots has on pesticides applied in the field. We found that activity in the roots of corn planted in the field greatly contributed to the breakdown of pesticides applied to soil to less harmful forms of the chemicals. The roots support high populations of microorganisms that consume the pesticides and actually use them as a source of food. The partnership of corn roots and root-inhabiting microorganisms contributes t the breakdown of chemicals applied to soil and greatly reduces the risk of these chemicals entering our water supplies.
Technical Abstract: Roots of crop plants support a higher and more diverse community of microorganisms than that found in bulk soil. The environment around roots, known as the rhizosphere, supplies nutrients to support microbial growth and likely influences degradation of soil-applied pesticides used in crop management. Several experiments using corn were conducted in the greenhouse and field to determine the effect of rhizosphere microbial populations on degradation of the insecticide carbofuran and the herbicide atrazine. The rate of degradation of carbofuran near corn roots was two to three times higher than in soil without roots. In the field, atrazine and carbofuran concentrations in the upper 10 cm of soil planted to corn were two times lower than in fallow soil 15 days after application. This observed rapid disappearance of atrazine from soil planted to corn could reduce potential transport of residual atrazine to surface and ground waters. Populations of carbofuran-degrading microorganisms were also thre to five times greater in rhizosphere soil than in soil without roots. Selected fungi from corn rhizospheres were able to use carbofuran as the only source of nutrients, indicating that these fungi contribute to carbofuran degradation in fields planted to corn.