The capacity of a manure-impacted soil to retain phosphorus (P) relates to risk of P loss from sandy soils to adjacent water bodies. A new concept to calculate the safe P storage capacity (SPSC) per unit volume of soil, based on the P saturation ratio (available P/Fe+Al), is used to predict the “safe lifespan” of a P-impacted soil under different intensities of animal operations. The SPSC was validated by a column study in which known amounts of P were added, reduction in soil capacity predicted, and compared to the actual SPSC calculated at the end of the column experiment by analyzing soil oxalate-extractable P, Al, and Fe. Important field applications of the SPSC concept would include: i) predicting the reduction in SPSC of a soil with time if the P loading to a soil is known, ii) evaluating how much P can be safely applied to a soil before the soil becomes an environmental risk if manure application is based on nitrogen requirements of a crop instead of P requirements, iii) using SPSC as a parameter in the Florida P-Index as a replacement for soil test P, iv) using SPSC to calculate the amount of water treatment residuals to be added to a P-impacted soil without negative impact on plant growth, and v) identifying suitable areas for location of animal-based agriculture by selecting soils which have a greater capacity to retain P.