Technical Abstract: Concern over the enrichment of agricultural runoff with phosphorus (P) from land applied livestock manures has prompted the development of manure amendments that minimize P solubility. We evaluated the effect of mixing two rare earth chlorides, lanthanum chloride and ytterbium chloride, with poultry, dairy, and swine manure on P solubility in the manure as well as on the fate of P when the manure was applied to soil and subject to a runoff experiment. In terms of manure P solubility, La:WEP ratios close to 1:1 resulted in maximum WEP reduction of 95% in dairy manure and 98% in dry poultry litter. Results from the runoff study showed that applications of rare earth elements to dry manures such as poultry litter were less effective in reducing DRP in runoff than in liquid manures and slurries, which was likely due to mixing limitations. The most effective reductions of DRP in runoff by rare earth elements were observed in the alkaline pH soil, although reductions of DRP in runoff from the acidic soil were still greater than 50%. Rare earth elements also showed a strong association with PP in runoff suggesting a potentially useful role in tracking the fate of P from manure amended soils. Finally, rare earth elements that remained in the soil following runoff had an apparent tendency to sorb additional soil P, especially in soils receiving manure amendments. The findings reported herein clearly have valuable applications in water quality protection and the evaluation of P site assessment indices.