Impact of Glyphosate Resistant Corn, Glyphosate Application, and Tillage on Soil Characteristics and Plant Nutrient Uptake.

Conservation tillage practices have been widely implemented using genetically modified (GM) glyphosate resistant corn (Zea mays L.) along with applications of the herbicide glyphosate. In a replicated split-split plot field study (tillage +/-, GM corn +/-, glyphosate +/-), we tested the hypothesis that long-term applications of glyphosate to both resistant and non-resistant corn under reduced and conventional tillage management would impact soil characteristics and nutrient uptake.  Commercial hybrids of either GM or non-GM corn were planted from 2008 to 2012.  In 2013, transgenic and non-transgenic corn isolines were planted in respective plots.  Previous to study establishment, GM crops (cotton Gossypium hirsutum L., soybean Glycine max. L.) were planted in the study area.  Soil was sampled at planting every year and assessed for various parameters, and crop yield was measured.  In 2013, a more comprehensive evaluation (soil physical, chemical, and biological; plant nutrient; plant disease) was conducted to assess effects of treatments after 5 years.  This paper reports results of the 5-year assessment.