WATER-EXTRACTABLE PHOSPHORUS REDUCTION IN POULTRY LITTER WITH CALCIUM- AND IRON-RICH BYPRODUCT AMENDMENTS

Abstract

In the poultry producing regions of Delaware, Maryland, and Virginia, long-term application of poultry litter as the primary crop nitrogen source has resulted in elevated soil phosphorus (P) levels and is suspected of being a source of dissolved phosphorus in surface waters. Dissolved P is the most readily available form for algal uptake in receiving waters, and hence may disproportionately contribute to eutrophication. One potential solution to this problem that would allow farmers to continue land applying poultry litter is to amend manure with high P-affinity materials. Two high P-affinity materials produced in the titanium dioxide manufacturing process, secondary gypsum (SG) and filter cake (FC), were investigated as potential poultry litter amendments. Both are rich in iron, and SG also contains a significant quantity of calcium and sulfates, primarily in the form of gypsum. Laboratory experiments were conducted to investigate: (1) the appropriate ratio of litter to amendment, (2) the effect of 1, 2, and 4 week incubations on soluble P, and (3) the effect of amendments on poultry litter pH. Four treatments were investigated: (1) poultry litter only, and poultry litter amended with: (2) SG, (3) FC, and (4) a mixture (MIX) of SG and FC. The pH of the amended poultry litter decreased from an initial pH of 8.3 to a pH of 6.2 to 7.0. Amendment- to-litter ratio had the most profound impact on water-extractable phosphorus (WEP). All treatments significantly reduced WEP as compared to the control samples. Poultry litter to amendment mixtures at a 1:1 (mass basis) rate reduced WEP by 98%. The reduction dropped to 90% for the 2:1 mix, approximately 74% for the 4:1 mix, and 40% to 60% for the 8:1 mix.