Nutrient, Sediment and Herbicide Runoff Impacts From Conventional and Conservation Tillage Systems Under Furrow Irrigation.

Conservation tillage is widely practiced in many areas of the U.S. to prevent soil erosion, reduce nutrient loading and conserve soil moisture. However, the practice has far lower adoption rates among producers utilizing furrow irrigation, especially in the western U.S. and Colorado. This study compared three different tillage systems, conventional till (CT), minimum till (MT), and strip till (ST) under furrow irrigated grain corn (Zea mays), managed on farm-scale sized plots in northeastern Colorado.  Water runoff samples were collected in each plot at the bottom of the field during six and 11 irrigation events during the 2011 and 2012 growing seasons, respectively. Runoff water was sampled at 0, 120, and 240 minutes after initial water runoff using small weirs installed at the end of the furrows. Water quantity was determined using furrow flumes to determine total runoff volume and to calculate loads for each measured parameter. Laboratory analyses of these samples were conducted to quantify total phosphorus and nitrogen, ortho-P, nitrate, sediment, atrazine and s-metolachlor concentrations.  Tillage systems did not consistently affect nutrient and sediment concentrations in runoff. The herbicide s-metolachlor had reduced concentrations in conservation tillage plots in 2011, but not in 2012. Atrazine was unaffected by tillage treatment.