The Contributions of Nitrogen and Irrigation Management in Reducing the Risk of N Leaching in Florida Potato Production.

Abstract: The goal of sustainable management of nitrogen (N) in agricultural systems is to minimize N lost to leaching by ensuring best management of nitrogen and irrigation programs. This is relevant in Florida, with significant water quality issues and coarse textured soils with low water-holding capacities. Fertilizer is the major source of N for potato production, but water is the driver of N leaching. Understanding the contribution of nitrogen and irrigation management strategies in the reduction of leaching losses is critical for reducing the environmental impacts of Florida potato production. We hypothesize that using controlled-release N fertilizer and maintaining the soil moisture slightly below field capacity would reduce the risk of N leaching by minimizing the N concentration in the soil pore water and providing a soil water reservoir to store rainwater. We used drainage lysimeters to measure N leaching in potato production under a combination of irrigation and nitrogen practices on an Entisol in Citra, FL. Treatments consisted of three nitrogen management programs (soluble N at 224 kg ha-1 N from a urea-ammonium nitrate mixture, or 224 or 168 kg ha-1 N from polymer-coated urea) and three irrigation treatments (maintaining soil moisture at field capacity with daily irrigation at 125% ET or 100% ET, or maintaining soil moisture between 50 and 75% field capacity). All possible combinations of treatments were arranged in a completely randomized design with three replicates. For the soluble-N treatment, 10% of the N was applied immediately prior to planting, with the remainder evenly split at plant emergence and 44 days after planting. For the polymer-coated N treatments, 100% of the fertilizer was incorporated in the bed immediately prior to planting. Irrigation was applied by sprinklers based on checkbook scheduling. We measured potato plant dry matter bi-weekly in the growing season and nitrate-N leaching loads were calculated from leachate volume and N concentrations in the leachate.