Manure Phosphorus Fractions: Development of Analytical Methods and Variation with Manure Types

A contribution of the University of Nebraska Agricultural Research Division, Lincoln, Nebraska. journal series no. 14475.

Abstract

Manure phosphorus (P) extraction and storage procedures were evaluated, and manure types were characterized for extractable P. The objectives of this research were to evaluate manure P extraction and sample storage procedures and to characterize manure types for water‐extractable P (WEP) and NaHCO₃ P (BiEP). Manure P was extracted at dry matter–to–water extraction ratios of 0.5 g/200 mL, 2 g/200 mL, 2 g/20 mL, and 20 g/200 mL. Shaking times of 0.5 h, 1 h, or 2 h were evaluated along with filter paper types (Whatman No. 42, Whatman No. 40, and 0.45‐µm). Single or sequential extractions and repeated extractions with water or NaHCO₃ were also compared on various manure sources. Manure types were treated as replications in the analysis of variance to reduce the probability of making a Type I error in applying the results to diverse manure types. Dry matter–to–water extraction ratios more concentrated than 1 g/100 mL removed less P than extraction at 1 g/200 mL, which removed a similar percentage of total P (TP) as 0.5 g/200 mL ratio. A single extraction with a 1 g/200 mL or more dilute ratio with 1 h of shaking time was found to give a good estimate of extractible P. Extracted manure P was similar for three sequential extractions of 1 g/100 mL dilution ratio compared to one extraction with 1 g/300 mL. Filter paper type did not affect the amount of P extracted. Phosphorus extraction was more consistent with samples stored dry as compared to refrigerated or frozen conditions. Extractible P in swine manure, as a percentage of TP, was more than for other manure types.

Keywords:

• Dilution ratios
• extractible P
• filter paper
• shaking time

Acknowledgment

This publication was made possible through support provided by the U.S. Agency for International Development, under the terms of Grant No. LAG‐G‐00‐96‐900009‐00.

Notes

A contribution of the University of Nebraska Agricultural Research Division, Lincoln, Nebraska. journal series no. 14475.