Availability, efficiency, and fate of alternative nitrogen sources in seepage irrigated potato production

Vegetable crop production in the Tri-County Agricultural Area (TCAA) consisted of approximately 11330 ha irrigated vegetable cropland predominated by cabbage (2n=18; Brassica oleracea L.) and potato (2n=48; Solanum tuberosum L.) crops. The current nutrient losses associated with agriculture system are due to combined factors such as sandy soils, perched water tables, and unpredictable rainfall. Also, high fertilization rate is a concern for future sustainable development and environmental quality. Best Management Practices (BMPs) have been implemented in the TCAA to help growers apply alternative agricultural practices to remain profitable while reducing the negative impact of environmental quality, especially water quality.;The controlled-release fertilizers (CRF), as one potential component of BMPs, were evaluated for their influence on potato production, tuber quality, and water quality. The research objectives were to: 1) characterize a nutrient release profile of CRFs under laboratory and field conditions; 2) determine the influence of CRF programs on potato production, tuber quality and water quality; 3) compare nutrient use efficiency of several fertilizer programs and; 4) estimate in-row soil nutrient movement of several fertilizer programs for northeast Florida potato production.;This research was divided into three sub-experiments: CRF evaluation under a controlled system, field evaluation of CRF, and a nutrient in-row movement study. Release profiles of several fertilizer sources were evaluated under controlled constant and variable temperature. P-PSCU (polymer sulfur-coated urea, 420 g N kg-1, Purcell Technologies, INC) and H-PCU2 (polymer coated urea, 420 g N kg-1, Haifa Chemical, LTD) were potential fertilizer candidates to synchronize the N demand of potato crop at northeast Florida production. The linear formula (K=AT+B) developed in this study described the relationship directly between release rate (K) and temperature (T), where A and B are constants. The protocols of CRF evaluation developed from this study can successfully determine the fertilizer release profile prior to field application.;The field study evaluated alternative fertilizer program and potato cultivars on tuber production, tuber quality, and ground water quality. The results from CRF field evaluations demonstrated that PSCU (380 g N kg-1, Scotts LLC) and PCU (440 g N kg-1, Agrium INC) led to comparable total and marketable yields as compared to soluble N fertilizers. For 'Atlantic' and 'FL 2053', tuber yields were higher for plants fertilized with PSCU applied before and at planting or a PCU combination with AN sidedress compared to other fertilizer program. For 'Harley Blackwell', tuber yields were similar between different treatments, indicating more flexibility of fertilizer application. Though yields were lower, 'Harley Blackwell' and 'FL 2053' had greater resistance to tuber internal heat necrosis (IHN), a psychological disorder than 'Atlantic'. Plants fertilized with a liquid CRF program (urea formaldehyde) produced significantly lower total and marketable yields due to their slow release characteristics than plants with the AN treatment.;The nutrient in-row movement study demonstrated that plants fertilized with polymer sulfur-coated urea (PSCU, 380 g N kg-1, Scott LLC) or polymer coated urea (PCU, 440 g N kg-1, Agrium INC) produced higher total and marketable yields than plants fertilized with urea formaldehyde (UF) products under leaching events. Leaching water samples collected from plots fertilized with PSCU had the highest NO3-N concentration and loads (24.4 mg L-1 and 12.4 kg ha-1) since N release of PSCU was less temperature sensitive resulting in high N release in the early season. These results would support the use of PCU over PSCU as a CRF. A 5 cm rainfall at early growth (20-25 cm) and full-flower growth stages reduced soil NO3-N concentration below the sufficient range (tuber initiation: greater than 20 mg kg-1; tuber bulking: 15∼20 mg kg-1), resulting in yield losses. This indicated that plants fertilized with CRFs at 196 kg N ha-1 with two potential leaching events during growing season required supplemental N to avoid yield losses during a 100 day growth season.