Identifying hotspots of soil legacy phosphorus for soil P remediation on a cattle ranch in the Headwaters of the Everglades, South Central Florida, USA, 2020.

Phosphorus (P) cycling has been altered by human activities across various scales. 'Soil legacy P,' driven by agricultural changes such as excessive P fertilization and manure input, has led to P accumulation in soils. These legacy P reserves are long-term non-point sources, causing downstream eutrophication. Despite considerable scientific and policy interest, the fine-scale spatial heterogeneity, underlying drivers, and scales of variance of legacy P remain poorly understood. This dataset comprises of 1,438 surface soils sampled in 2020 across two typical subtropical grasslands managed for livestock production in South Central Florida, USA. The types of grasslands sampled were Intensively-managed or Improved pastures (IM), and Semi-native (SN) pastures. Chemical analysis was performed on the soil samples to determine three soil legacy P measurements (total P, Mehlich-1 and Mehlich-3 extractable P representing labile P pools) across the landscape. Other variables analyzed includedsoil organic matter, pH, available Fe and Al. Additionally, aboveground biomass samples were collected at a subset of soil sites, and analyzed for P content. The key questions regarding soil legacy P related to: its spatial variability and hotspots, variance distribution, relationship to land management and soil characteristics, and correlation with aboveground plant tissue P concentration. Subsequent analysis and spatial autoregressive modeling from this dataset revealed extreme variability of soil P at small scales, with diminishing variance as spatial scale increased, and increased variance in IM vs SN pastures. These findings enhance our understanding of the underlying drivers, spatial patterns, and variances of soil legacy P. Research suggests that broad pasture- or farm-level best management practices may be limited and less efficient, particularly for high-intensity pastures. Instead, management strategies to reduce soil legacy P could be implemented at fine scales, targeting P hotspots across the landscape. This approach could lead to more effective mitigation of downstream eutrophication and ecosystem services degradation caused by legacy P reserves.