Matching crop nitrogen (N) demand and supply is necessary to increase crop N use efficiency (NUE) and reduce environmental impact. Proximal optical sensors such as the Soil Plant Analysis Development (SPAD) meter have been found to be useful in monitoring the crop N status, providing insight into the effects of N fertilization practices in cropping systems. High N rate applications are common in conventional tomato production, where loss of N, more specifically NO 3 - , from the rootzone can decrease water quality. Thus, optimal N management of fertigated vegetable crops requires frequent and rapid assessment of the crop N status to quickly adjust application of N when required. A two-year field study was conducted in north Florida to evaluate the crop N status based on N fertilization practices associated with soluble urea and polymer coated controlled-release urea (CRU) for fall and spring tomato (‘HM 1823’) grown in sandy soils under a plastic-mulched bed system. In addition to a no N fertilizer treatment, three urea N sources [one soluble source and two polymer-coated CRU sources with different N release durations of 60 (CRU-60) and 75 (CRU-75) days] were applied at three N rates (140, 168, and 224 kg ha -1 ), where 224 kg ha -1 is the recommended N rate for tomato production in Florida. Soluble urea was split applied weekly over the 13-week growing season, whereas CRUs were applied at the full rate once at preplant. For all seasons, biweekly SPAD meter readings were taken and sampling periods coincided with the vegetative, flowering, fruit set, fruit growth, and harvest growth stages. Overall, minimal differences in tomato N status were observed among the tested N rates and N sources, indicating that all N fertilizer practices tested maintained similar N use. Thus, irrespective of the N source, this study found that tomato N demands could be met at a 38% reduction of the recommended N rate, potentially enhancing NUE in tomato production systems cultivated on sandy soils in north Florida.
