Yield and Soil Leaching Responses of Vegetables to Conventional and Slow Release Nitrogen Fertilizer Applications.

Sound fertilizer management strategies are critical in coarse textured soils where irrigated production often lead to water and soil contamination.  Such fertilizer leaching potential coupled with higher fertilizer and energy costs have led to an increased interest in the use of slow-release fertilizer (SRF).  When applied pre-plant as a single application, SRF formulations are expected to reduce production costs, limit nutrient leaching, and sustaining crop production, thereby enhancing nutrient use efficiency.  A field study was conducted on a sandy loam soil to evaluate the effects of a soluble nitrogen (N) fertilizer, Urea Ammonium nitrate, and a SRF formulation on the yields of two vegetable crops and on nitrate leaching potential below the root zone.  Three N rates of SRF applied pre-plant were compared to six applications of soluble N at equivalent rates.  Petioles and soil samples were collected during the growing seasons to determine N status.  Results of the first experimental study conducted on fresh market tomato indicated that there was no significant difference (p < 0.05) in yield between the soluble and SRF fertilizers.  The sugar levels were also equivalent for both fertilizer types, indicating that the one-time SRF application did not affect crop yield and quality.  Post-harvest soil NO₃-N levels at 0-2 ft depth were lower than preplant levels, suggesting a low potential for N leaching below the root zone.  Findings observed for the second experimental study conducted on broccoli indicated similar results for crop quality and soil NO₃-N levels; however, there was a significant yield increase with SRF.  The single SRF application represented a potential saving in energy, fuel and labor compared to the multiple UAN applications traditionally used in vegetable production.