Douglas Carlson
Department of Geology and Geophysics, Louisiana State University, E235 Howe-Russell-Kniffen Geoscience Complex, Baton Rouge, Louisiana 70803

The Environmental Impact of No-Till Farming on Lower Mississippi River Quality

Groundwater and Environmental Case Studies (GRBCC, Room 332A)
Tuesday, September 22, 2015, 11:10 am

Mississippi River water quality has been studied for approximately 175 years. Many of these studies focus on total suspended sediment (TSS), and/or nutrients. There have been a number of changes to the river itself and the surrounding watershed that impacted water quality. One of the major changes that has recently occurred within the watershed is the adoption of no-till farming practice, mainly in the last 25 years. How, has this change impacted water quality?

Numerous studies indicate that no­till farming reduces sediment loss by approximately 80% to 100% and nutrient loss of 20 to 40%, when compared to conventional tillage practices. In the last three decades, millions of acres of cropland within the watershed have been converted to no-till cultivation practice. What has the change of TSS and nutrient concentration been at stations with long histories, generally over 30 years? For example, the concentration of TSS for the Mississippi River at New Orleans has fallen from typically 700 ppm in the 1920s, to 500 ppm in 1950s, to 200 ppm in 1970s, and to 100 ppm in 2010s. Changes through 1970 are largely the result of construction of control structures. However, these structures were largely completed by 1970. If so, why has TSS concentration been cut in half and there been a reduction in nutrients, even though sale and consumption of fertilizers has remained approximately constant over the past 30 years? The focus study is on results for the lower Mississippi River. However, dozens of sites within sub­watersheds throughout the Mississippi River watershed are examined in order to see if the changes within the full watershed are mainly a result of change in cultivation practice towards no­till practice. This involved the comparison of concentrations prior to no­till farming in the 1970s to concentrations in last decade, using two different nonparametric statistical tests of Median and Mann­Whitney Ranks.