Plant Influence on Soil Phosphorus Storage Capacity in Soils Receiving Alternative Fertilizers.

Phosphorus-impacted soils threaten water resources in many regions of the U.S.A., including Florida, but phosphate rock reserves are also dwindling. Reclaiming P as a slow-release fertilizer from municipal waste water treatment in the form of struvite, biosolids, and biochar derived from biosolids, may reduce our reliance on phosphate rock reserves and lessen agricultural P losses compared to more conventional, soluble P fertilizers. A column experiment was conducted in a greenhouse using two commonly occurring Florida soils (Spodosols and Ultisols). Class AA and B biosolids, as well as biochar prepared from Class B biosolids represented organic P sources, and were compared to inorganic P fertilizer sources, struvite and conventional triple super phosphate (TSP), applied at 45 kg P₂O₅ ha^-1. Bahiagrass Paspalum notatum Flüggé biomass was harvested four times and analyzed for P and other plant nutrients. After 5 months, unplanted and planted column soils were analyzed for Mehlich-3 P, Fe, Al, and water soluble P (WSP). The soil P storage capacity (SPSC) was calculated in order to assess potential environmental P risk. Plant P content was also analyzed. The SPSC values often became negative in unplanted columns, suggesting a greater potential for environmental P release while planted columns improved SPSC values. The slow-release P fertilizers led to lower P loss risk than using TSP. However, early harvest yields trended higher with the TSP and Class B biosolids treatments, while yields improved later in the season with struvite. All P fertilizers resulted in greater total biomass compared to the control treatment.