Manure phosphorus speciation and transformation in an acidic environment
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Phosphorus (P) is an important nutrient for crops and livestock and is commonly present in animal manures. Consequently, animal manures have been broadly applied to agricultural lands as fertilizer. However, long-term manure application to soil may lead to P losses through surface runoff with potential impairment of surface waters. The objectives of this dissertation were 1) to develop an animal manure P extraction method that simulates P release in acidic soils, 2) to identify P compounds extracted from broiler litter by various extractants at different pH levels, and 3) to evaluate the effects of temperature and water content on release of broiler litter P during storage. Broiler litter, layer manure, and dairy slurry samples were extracted with water or MES buffer (2-(N-morpholino) ethanesulfonic acid at pH 6) at three manure:extractant ratios (10:1, 100:1, or 200:1) and three extraction times (1, 4, or 24 h). In most cases, extraction with MES buffer removed larger amounts of Total Dissolved P (TDP), Dissolved Reactive P (DRP), and Bioavailable P (BAP) than extraction with water. Likewise, widening the water to manure ratio (10:1 to 200:1) as well as extending the extraction time from 1 to 4 or 24 h usually increased the amount of TDP, DRP, and BAP extracted. A P fractionation study of broiler litter and layer manure indicated that the major P fraction was MES-P, and that the P species present were highly associated with Ca and Mg 31cations. Results from P Nuclear Magnetic Resonance (NMR) analysis found that significant amounts of orthophosphate and phytate were extracted from broiler litter and layer manure. A laboratory incubation of broiler litter at three temperatures (10, 20, or 30°C) and three -1water contents (400, 800, or 1200 g kg) showed that incubation brought about an increase of TDP in the MES fraction across all water contents and temperatures. This change resulted from a transfer of TDP from the NaHCO3, NaOH, and Residual P (RP) fractions to the MES fraction. Microbial activity played an important role in P transformation during the incubation, and in most cases a shorter storage term resulted in a smaller release of soluble P than a longer storage.