Phosphorus fertilization increases fresh-market tomato yield in Central Florida sandy soils testing high in Mehlich-3 phosphorus

Phosphorus (P) fertilizer recommendations for fresh-market tomato production in Florida are based on soil test interpretations using the Mehlich-3 extraction method, where soil P concentrations exceeding 45 mg kg –1 are classified as high and additional P is not recommended. In Central Florida, sandy soils on many commercial farms frequently test high in Mehlich-3 P, yet tomato yield responses to supplemental P have been observed under commercial production conditions. A study was conducted as part of a statewide nutrient management initiative to evaluate the reliability of current P recommendations and to assess whether Mehlich-3 soil test P adequately reflects crop response to fertilization in these systems. Five on-farm trials were conducted over three years to evaluate the effects of P 2 O 5 rates (≤224 kg ha –1 ) on soil P extracted by different soil tests (Mehlich-1, Mehlich-3, Bray, Olsen, and Water), total marketable yield, P uptake, and fertilizer P use efficiency. Results demonstrated a consistent linear increase in total marketable yield, averaging 21% in four of the trials, with increasing P 2 O 5 rates, despite the Mehlich-3 P > 45 ppm. Although phosphorus uptake also increased linearly with P 2 O 5 rates, P use efficiency was maximized at 112–168 kg ha –1 P 2 O 5 . Overall, all soil P extractants significantly correlated with yield. Nevertheless, Olsen and Mehlich-1 more clearly reflected fertilizer-induced changes and yield responses. Finally, we found that Mehlich-3 overestimated available P, accounting for more than 80% of total soil P. These findings provide evidence that tomato yield may still respond to supplemental P fertilization under commercial production conditions in high-testing sandy soils of Central Florida, supporting further reevaluation and calibration of current soil test interpretations and P recommendations.