Plant, surface water, and lysimeter data suggest potential for groundwater upwelling being a major P source in a Florida ranchland, 2021-2024

Vegetation harvest is a promising strategy for reducing phosphorus (P) losses from agricultural systems enriched by historic fertilizer use. We evaluated the phytoremediation potential of hay fields at Archbold Biological Station’s Buck Island Ranch, Florida, using three forage species: Paspalum notatum (Bahia grass), Hemarthria altissima (Limpo grass), and Cynodon nlemfuensis (Star grass). Among these, H. altissima exported the greatest amount of P in harvested biomass, removing 19.8 ± 1.62 kg P/ha in 2022, compared with 6.45 ± 0.33 kg P/ha for P. notatum and 4.91 ± 0.22 kg P/ha for C. nlemfuensis. Drainage ditches in hay fields contained, on average, 58.97% less P than those in grazed pastures (p < 0.05). This reduction was associated primarily with lower water accumulation in hay field ditches (16.7 ± 0.7 cm) than in pasture ditches (24.5 ± 0.8 cm). In addition, seasonal groundwater upwelling increased total phosphorus concentrations in subsurface lysimeters beneath grazed pastures by 214% (p = 0.003), whereas this signal was absent beneath hay fields, suggesting that hay production may intercept upwelling P before it enters surface waters. Despite substantial P export in harvested biomass, topsoil P concentrations remained stable (50–60 mg/kg total P), indicating that subsoil P mobilized during flooding may help sustain continued P removal. Together, these results show that hay fields can reduce surface water accumulation, limit ditch P loads, and export legacy P in biomass in historically fertilized pasture systems, with H. altissima emerging as the strongest phytoremediation candidate. Incorporating subsurface P dynamics into land management may therefore improve the effectiveness of strategies aimed at reducing legacy P and enhancing water quality in agricultural landscapes.