Using rare earth elements to control phosphorus and track manure in runoff

Area of Science:

• Environmental Chemistry
• Soil Science
• Agricultural Science

Background:

• Agricultural runoff, particularly phosphorus (P) from livestock manures, enriches water bodies.
• Manure amendments are being developed to minimize P solubility and reduce environmental impact.

Purpose of the Study:

• To evaluate the efficacy of rare earth chlorides (lanthanum and ytterbium) as manure amendments.
• To assess the impact of these amendments on P solubility in various manures.
• To investigate the fate of P and rare earth elements (REEs) in soil and runoff after manure application.

Main Methods:

• Amending poultry, dairy, and swine manures with lanthanum chloride and ytterbium chloride.
• Laboratory incubation to measure P solubility.
• Surface application to soil boxes followed by simulated rainfall to assess runoff.
• Analysis of P and REE concentrations in manure, soil, and runoff.

Main Results:

• La:water-extractable P (WEP) ratios near 1:1 maximally reduced WEP by 95% (dairy) and 98% (poultry litter).
• REEs were less effective in reducing dissolved reactive phosphorus (DRP) in runoff from dry manures due to mixing limitations.
• DRP reduction in runoff was most effective in alkaline soils (>50% reduction in acidic soils).
• Particulate REEs associated with particulate P in runoff, suggesting a tracking role.
• Residual REEs in soil precipitated WEP, particularly in amended soils.

Conclusions:

• Rare earth element amendments show significant potential for reducing phosphorus solubility in livestock manures.
• REEs can effectively reduce dissolved reactive phosphorus in agricultural runoff, especially in alkaline soils.
• The association of REEs with particulate P offers a method to track manure constituents in the environment.
• These findings support applications in water quality protection and P site assessment.