Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 2, 2000
Publication Date: February 5, 2001
Interpretive Summary: Offsite land application of animal manure is the major avenue for disposing of the large volume of manure produced by concentrated animal feeding operations. Manure still contains large quantities of plant nutrients in both inorganic and organic forms in partial state of decomposition. A major ecological problem is the potential release of high levels of phosphorus in manure that can cause the degradation of air quality and the water quality of streams, lakes, reservoir and estuaries in watersheds with intensive animal feeding operations. To maintain the option of manure application on croplands, the manure soluble reactive N and P levels must be reduced to bring the N to P ratio to correspond more with that needed for crop growth. The chemical fractionation study showed that two mineral by-products that are rich in aluminum and iron were very effective in immobilizing soluble reactive P and the iron-rich industrial by product was superior to the aluminum-rich drinking water treatment residual. Composting diminished manure volume and did not enhance the immobilization of soluble P in both untreated manure and in by- product-amended manure. However, composting may have induced internal changes in the water-insoluble P fractions that reduce the eventual release of P in manure compost.
Technical Abstract: Shifts in manure P chemical forms and pool sizes induced by water- treatment residuals and industrial mineral by-products are largely undefined. We conducted a manure P fractionation study to determine mechanisms of reduction in soluble-reactive P (SRP) in poultry manure upon mineral by-product additions. The effect of composting on the P immobilization efficacy of the by-products was also determined using laboratory self-heating composting simulators. The mineral by-products included an aluminum-rich water-treatment residual (Al-WTR) and an iron-rich titanium processing by-product that were added to raw poultry manure. The non-composted manure averaged 11% of the total P content as SRP forms. The by-products significantly reduced manure SRP, by an average of 39 and 48% in the Al- and the Fe- treated manure, respectively. The by-products also reduced the 0.5 M NH4F-extractable P (FEP) fraction. Shifts in P forms between FEP and 0.1 M NaOH- extractable P (SHEP) depended upon the Al and Fe content of the by- products while the combined FEP + SHEP pool remained constant. Phosphate sorption measurements supported the observations that showed that the Fe-rich by-product was generally more effective at reducing manure SRP than the Al-WTR and enhancing the formation of SHEP forms at the expense of FEP. Composting had no detectable effect on the efficacy of immobilization of manure SRP by the mineral by-products. Potential mechanisms of enhanced stabilization of P included chemical shifts from SRP and FEP to citrate-bicarbonate-dithionite extractable P fraction. Therefore, the choice of P immobilization agents strongly affected the eventual stability of immobilized P forms.