FORMS OF PHOSPHORUS IN MANURE AND THEIR RELEASE DURING RAINFALL

Authors: Sharpley, Andrew; Moyer, Barton

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2000
Publication Date: 6/20/2000
Citation: Sharpley, A.N., Moyer, B.G. 2000. Forms of phosphorus in manure and their release during rainfall. Journal of Environmental Quality. 29:1462-1469.

Interpretive Summary: With the reduction of point sources of pollution over the last two decades, there has been an increased documentation and awareness of the contribution of nonpoint sources of nutrients (P and N) to impaired water quality in the U.S. This has focused attention on the role of agricultural nonpoint sources of P and N. In many cases, an increased number of animal feeding operations in localized areas has led to an accumulation of nutrients in manure that exceed crop needs. For P, the continual land application of manure has increased the potential for P enrichment of agricultural runoff. The greater inputs of P to fresh waters have been linked to the incidence of harmful algal blooms and noxious chemical production during drinking water chlorination in several areas of the U.S. However, not enough information is available on the amounts and forms of P in manures and composts, in order to develop sound nutrient management strategies. This study of several types of manures and composts showed that a simple and rapid extraction of manure with water provides an estimate of the relative ability of these materials to enrich runoff with P.

Technical Abstract: The large accumulation of P in manure from animal feeding operations in localized areas has increased the potential for P export following land application. Impairment of freshwater quality by accelerated eutrophication has led to the development of P-based manure management guidelines. To develop scientifically sound guidelines, we investigated the amounts and relative solubilities of P in manures and their composts using a modified Hedley fractionation and release of P during rainfall (6.5 cm/hr for 30 min). Twenty-four samples of dairy manure, dairy compost, poultry manure, poultry compost, poultry litter, and swine manure, collected over two years, ranged in total P concentration from 2600 to 40000 mg/kg. Most P was inorganic (63 to 92%) with the relative distribution in inorganic and organic fractions a function of manure and compost type. In dairy manure, 80% of inorganic P was water extractable (2030 mg/kg), while 55% was hydroxide extractable in swine slurry (16620 mg/kg). The dissolved inorganic P concentration in leachate from manure and compost (11 tons/ha manure application rate) during a 30-min rainfall ranged from 34 (poultry litter) to 75 mg/L (poultry manure). The amount of P leached by five rainfalls was closely related to respective water extractable inorganic (r2 of 0.99) or organic P (r2 of 1.00) of each material. This suggests that water extractable P may be used to estimate the potential for land-applied manures or composts to enrich leachate and surface runoff P.