Tillage and N Management Practices Impact Water Quality of Runoff Water in Irrigated Cotton Systems

Implementing efficient tillage and fertilization practices can reduce nutrient runoff in irrigated cotton systems. A factorial field study was conducted to quantify the impacts of furrow tillage practice and N fertilizer placements on nutrient losses in surface runoff water from irrigated cotton at the Judd Hill Foundation Farm in Trumann, AR. Soluble N and P content in water runoff were determined in the field that was plowed with either a 4” standard sweeps cultivator or a conservation plow (Furrow Runner), fertilized with either urea broadcast or 32% UAN side dressed at a rate of 90 N lbs acre^-1 (101 kg N ha^-1) and planted with ST4946 GLB2. Amounts of ammonium, nitrate, nitrite and phosphorus were measured in water samples collected during each irrigation event. Differences in ammonium (NH₄⁺), nitrate (NO₃), nitrite (NO₂) and phosphorus (PO₄) content in the water samples were observed during the early irrigation events. The highest levels of ammonium ions (0-1.107 mg L^-1) were measured where urea was applied regardless of tillage practice, while the highest nitrate concentrations (0-1.803 mg L^-1) were measured in conventionally tilled plots for both types of fertilizer N. Across all treatments, soluble P content was <0.2 mg L^-1. During the early irrigation events, there were variable trends in the impact of tillage and fertilizer forms on nutrient concentrations depending on sampling locations (i.e. top, no N, double N applied). Nitrate and ammonium ions were the highest among all nutrients measured during the first irrigation event. While our preliminary results show that conservation tillage and fertilization may have the potential to reduce nutrient losses in runoff water, water quality analyses of samples collected throughout irrigation events are still on-going to fully assess the trends and build-up of these nutrients in cotton fields managed with conservation tillage and fertilizer N practice.