UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Integrating soil conservation practices and glyphosate-resistant crops: impacts on soil
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2007
Publication Date: February 15, 2008
Citation: Locke, M.A., Zablotowicz, R.M., Reddy, K.N. 2008. Integrating soil conservation practices and glyphosate-resistant crops: impacts on soil. Pest Management Science. 64:457-469. DOI: 10.1002/ps.
Interpretive Summary: Farmers use conservation practices like no-tillage to reduce economic inputs, decrease runoff and improve soil conditions. Glyphosate resistant crops are compatible with either conservation or conventional tillage practices. Although environmental effects of glyphosate resistant crops or conservation management have been evaluated separately in a number of studies, little is known regarding their combined environmental effects. A study was conducted in Stoneville, MS in which reduced tillage corn and cotton crops were rotated, and the effects of glyphosate resistant crops on soil characteristics was monitored. After three years of continuous glyphosate management, higher plant biomass during fallow months in fields used to grow glyphosate resistant corn likely contributed to increases in carbon and nitrogen stored in the soil. After five years, subtle and dynamic changes in microbial populations due to the use of glyphosate resistant crops were observed. Results from this study indicate that differences in soil chemical and biological properties that are attributable to the interaction of conservation management and glyphosate are transient in nature and are either beneficial or environmentally benign.
From an environmental perspective, conservation management (CM) practices such as reduced tillage help improve soil conditions. Literature concerning effects of CM on the environment is building, and many of those studies include glyphosate resistant crops (GRC) or glyphosate as a management component. Media reports and commodity publications often cite environmental benefits derived from GRCs, and the compatibility of CM and GRC is usually credited. However, virtually no scientific data have been published evaluating the joint impacts of CM and GRCs on environmental quality. The assumption is that by implementing CM, the same positive impacts on soil and water are conferred whether or not GRCs are used. In this paper, we draw upon available literature from both CM and GRCs to provide an analysis of potential impacts on soil and water quality. Results from a six-year reduced tillage study in Stoneville, Mississippi, complement this paper's theme, as some differences in soil characteristics due to GRC management were observed. Plots managed under continuous GR maize (Zea mays) maintained greater soil organic C and N compared to continuous non-GR maize, but no differences were measured in continuous cotton (Gossypium hirsutum) or cotton rotated with maize. Soil microbial community structure based on total fatty acid methyl ester analysis indicated a significant effect of the GRC system on the microbial community following five years of continuous GRC compared the non-GRC system. Results from this study as well as the literature indicate that there may be differences attributable to the interaction of CM and GRC, but that they are transient in nature, and do not appear to convey harmful effects on the soil ecosystem.