Relatively high nutrient and water use by vegetable production systems can create conditions for nitrogen (N) and phosphorus (P) leaching that are more likely to impair surface and groundwater quality compared to other crop systems in Florida. Best management practices (BMPs) have been developed and recommended for improving surface and ground water quality while maintaining economic viability. However, the effects of most vegetable BMPs have not been quantified. A 3-year study was conducted in southern Florida to evaluate the effects of water-nutrient BMPs on crop yield, water use, and water quality. Three water-nutrient treatments were randomly applied among six hydrologically isolated 0.24 ha plots, which were planted with tomato (fall)-watermelon (spring) rotations. The water-nutrient management strategies compared were: 1) high fertilizer rate and irrigation input (HR) with seepage irrigation, which represents the current water and nutrient input by vegetable producers in south Florida; 2) recommended fertilizer rate and irrigation input (based on soil moisture) (RR) with seepage irrigation; and 3) same as the RR but with subsurface drip irrigation (RR-SD). Response variables tested were crop yield, water use, and N and P concentrations in soil and groundwater (shallow and deep). Field data were used to modify a lumped hydrologic model (ARCU2000) to simulate water table dynamics for plastic mulch raised bed conditions. The modified model was evaluated using measured water table depth beneath the crop bed surface.

No treatment effect on yield was detected for the entire study period, except for watermelon during a relatively wet spring 2005 crop season. The yield for spring 2005 for HR (38.7 Mg ha^-1) was statistically greater than the yield from RR (21.6 Mg ha^-1) and RR-SD (24 Mg ha^-1). Soil solution analysis revealed that N concentrations within and below the crop bed were significantly higher for HR compared with RR. Weekly to bi-weekly soil N concentrations in deep core (0–20 cm) soil samples were used to estimate the amount of N leached to the groundwater. Soil N leaching for HR was 60% greater than that from RR. Shallow groundwater quality data indicated that total N (TN) and P (TP) concentrations were significantly higher in HR (TN=38 mg/L, TP=3.1 mg/L) compared with RR (TN=16 mg/L, TP=2.1 mg/L) and RR-SD (TN=21 mg/L, TP=2.0 mg/L). However, no treatment effect was detected for deeper groundwater N and P concentrations. Results from the model evaluation showed that the modified model under performed (i.e., Nash-Sutcliffe coefficient = -0.67) in simulating water table depths. The model’s performance was limited by its daily time step. Use of a sub-daily time step is likely to improve the model’s performance.

Overall, use of recommended fertilizer and irrigation input for vegetable production in southern Florida can improve groundwater quality while maintaining crop yields under average weather conditions. Adverse impact on yield is likely under unusually wet growing conditions and may justify the application of additional fertilizer. The water table dynamics beneath these vegetable production systems can be simulated using lumped hydrological models.