Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2017
Publication Date: 1/4/2018
Publication URL: https://handle.nal.usda.gov/10113/6472230
Citation: CJenkins, M., Locke, M.A., Reddy, K.N., McChesney, D.S., Steinriede Jr, R.W. 2018. Glyphosate applications, glyphosate resistant corn, and tillage on nitrification rates and distribution of nitrifying microbial communities. Soil Science Society of America Journal. 81(6):1371-1380.
Interpretive Summary: Planting corn that has been genetically engineered to resist the herbicide glyphosate and glyphosate applications to fields to control weeds has become a wide-spread management practice for implementing reduced tillage across the USA. ARS scientists in Oxford and Stoneville, MS, designed and implemented a seven year-long field experiment in the Mississippi Delta to determine if this management practice would affect the process of nitrification, the microbial mediated process that converts ammonia to nitrate, and the soil microbial communities that initiate the process. Results of this study indicated that glyphosate applications appeared to inhibit nitrification in both bulk and rhizosphere soil environments. Continuous long-term applications of glyphosate to control weeds, thus, appeared to affect this naturally occurring microbial community. These results indicated that glyphosate may have a variable suppressive effect on the nitrification process under both conventional tillage and no-till.
Technical Abstract: Conservation tillage practices have combined genetically modified glyphosate resistant corn crops along with applications of the herbicide glyphosate. We tested the null hypothesis that the soil process of nitrification and the distribution of archaeal and bacterial nitrifying communities would not be impacted after six and seven years of glyphosate applications to glyphosate-resistant (GR) and non-glyphosate-resistant corn (nonGR) under conventional tillage and no-till. Nitrification potential activity rates of bulk soil and rhizosphere soil were determined. Copy numbers of total archaeal and bacterial components of the soil microbiomes, as well as archaeal and bacterial ammonia monooxygenase genes (amoA) were determined using quantitative polymerase chain reaction methodology. In 2013, the nitrification rate of the nonGR corn with no glyphosate application treatment associated with bulk and rhizosphere soils under no-till displayed greater (P < 0.05) nitrification rates than GR corn with glyphosate applications. In 2014, the nitrification rate of the rhizosphere soil under no-till in GR corn with no glyphosate application treatment was greater (P < 0.05) than other rhizosphere soil treatments. Ratios between archaeal and bacterial amoA genes indicated distinct dominance of ammonia oxidizing archaeal (AOA) communities in the rhizosphere soil. The ratios between AOA and ammonia oxidizing bacterial (AOB) amoA genes in bulk soil were more balanced. Glyphosate applications appeared to have an inconsistent inhibitory effect on nitrification. Importance: Glyphosate is widely and repeatedly used in GR corn for weed management. The field study presented was designed in part to determine the effects of repeated glyphosate applications under conventional tillage and no-till on the soil archaeal and bacterial communities that initiate the nitrification process.