Wastewater Chemistry and Fractionation of Bioactive Phosphorus in Dairy Manure

Abstract

Because manure organic phosphorus (P) is environmentally bioactive, a novel in situ enzyme hydrolysis assay was developed to identify water soluble‐ and labile complexed P and mechanisms controlling P solubilization in dairy manure. Water‐extractable P averaged 16% (±14.8%) of total P of 107 manures collected across five northeastern states of the USA. Adding a multidentate ligand solubilized inorganic complexed P (15±8.3%) primarily associated with calcium (Ca) and magnesium (Mg). An additional organic fraction (35.9±15.6%) was hydrolyzable by fungal phytases. The assay was more revealing about on‐farm P management than just knowing total P; the water‐extractable P distribution was skewed to the left, and two thirds were <2500 mg kg⁻¹; bioactive and total P were normally distributed, differing extensively between farms with a range spanning an order of magnitude. The assay's simplicity and robustness over the wide range of manure characteristics may increase routine evaluation of whole‐farm accumulation of environmentally sensitive P forms.

Keywords:

• Animal manure
• bioactive phosphorus
• ligand exchange
• phosphorus fractionation
• phytase‐hydrolyzable phosphorus
• phytic acid

Acknowledgments

The authors sincerely acknowledge the technical assistance of Bob Ransom during the conduct of the study.

Notes

*The mention of a trade or manufacturers name is made for informational purposes only and does not imply an endorsement, recommendation, or exclusion by the USDA‐Agricultural Research Service.