Phosphorus fertilizer thresholds matching snap bean nutrient demands in Florida Spodosols

Phosphorus (P) is a macronutrient essential for plant growth and development; however, its bioavailability is often limited in Florida Spodosols due to high soil acidity, low organic matter content, and strong sorption to aluminum (Al) and iron (Fe) oxides—particularly Al, which is often present at concentrations significantly higher than Fe. This study aimed to determine the optimal P fertilizer rate required to maximize snap bean (Phaseolus vulgaris L.) productivity while minimizing environmental risks in these challenging soil conditions. Field trials were conducted over two consecutive fall seasons (2022 and 2023) using a randomized complete block design. Treatments included five P₂O₅ rates (0, 45, 90, 134, and 179 kg ha⁻¹) in the first year and two additional rates (224 and 269 kg ha⁻¹) in the second year. Data on plant biomass, pod yield, chlorophyll content, P uptake, and soil P availability were collected and analyzed. Results showed that increasing P rates improved plant performance metrics, with diminishing returns observed beyond a certain threshold. Pearson’s correlation and principal component analyses revealed strong positive relationships among P application, crop physiological responses, and soil P dynamics. Using three response models—Mitscherlich-Bray, quadratic, and quadratic linear plateau—the estimated critical P₂O₅ threshold was 202 kg ha⁻¹, with an optimal range of 191–218 kg ha⁻¹. These findings support the development of science-based, site-specific P best management practices to enhance snap bean yield while mitigating environmental risks in subtropical agroecosystems.