Characterization of Phosphorus in Poultry Litter and Determination of Phosphorus Extraction Efficacy of Extractants
Type of DegreeMaster's Thesis
Crop Soils and Environmental Sciences
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Poultry litter (PL) is used as a nutrient source for row crops, horticultural crops, and pasture production. Typically, PL is a mixture of poultry feces, bedding materials, spilled grain and feather than can potentially enrich soils with primary nutrients [nitrogen (N), phosphorus (P), potassium (K)), and secondary nutrients [sulphur (S), aluminum (Al), iron (Fe), calcium (Ca), magnesium (Mg)]. Poultry birds lack phytase enzyme, hence they are unable to digest complex organic molecules such as phytic acid present in the feeds. This leaves greater proportions of undigested P in the bird’s feces. Additionally, PL is bulky and has low density which causes its long distance transportation uneconomical. This practice results in repeated land application of PL and increases the soil background P levels. Runoff losses from these P hotspots can cause eutrophication and aggravate water quality issues in the surface waterbodies. Therefore, there is a need to understand the P forms present in PL and develop methods towards extracting and recycling P safely for agricultural purposes. The overall goal of this study was to investigate different P forms present in litter and determine the P extraction efficiency of various chemical reagents to extract P from PL. Specific objectives of this study was to i) quantify various P fractions in poultry litter of four PL clean out frequencies (CF) (0-6 months, 6-12 months, 12-24 months, and 5-year-old) using sequential P fractionation ii) understand the difference in P forms among 4 CF of PL iii) to quantify the phosphorus dissolution efficacy of selected acidic (HCl, citric acid), neutral (water), and basic extractants NaHCO3 iv) quantify the co-release of metals during the extraction cycle. Sixteen PL samples were collected from eight counties in Alabama. Dried and ground PL were used for general chemical characterization and sequential P fractionation. 0.3g of PL was extracted using 30ml of de-ionized water (DH2O), sodium bicarbonate (0.5 M NaHCO3), sodium hydroxide (0. 1 3 M NaOH), and 1 M HCl in a sequential order. Total P in PL was characterized as DH2O P, NaHCO3- P, NaOH-P and HCl-P and residual P fractions, where each fraction represent P of increasing stability. Results showed that greater residence time of PL in the poultry house caused recalcitrant organic fraction to decline with time possibly due to the breakdown of organic P. Whereas, in 6 months old PL, the recalcitrant P was significantly greater than 5 year old PL, there was no significant difference in inorganic P fraction (Pi) between PL of different clean out frequency. Repeated independent extractions were performed with 4 selected acid and basic extractants: de-ionized water (DH2O), NaHCO3 HCl and citric acid. 0.3g PL was repeatedly extracted with 30ml of individual extractant. Filtrates were analyzed for dissolved total P (DTP) and molybdate reactive P (MRP). Co-release of nutrients and heavy metals were recorded with P release (Al, Fe, Ca, Mg, As, Cs, Cd, K, S). Acids like HCl and citric acids took 4 extraction cycles to extract upto 90% of the P, whereas NaHCO3 took 5 extraction cycle and extracted only 56 %. Similarly, deionized water took 7 extraction cycles and extracted 40% P. Comparing the DTP and MRP recovery rates of the acidic and basic extractants, HCl recovered significantly greater percentage (95%) of DTP, whereas citric acid recovered significantly greater percentage (66%) of MRP .The phosphorus extraction efficiency can be ranked as 1 M HCl > 1 M citric acid > 0.5 M NaHCO3> deionized water. The residual P left after water and sodium bicarbonate extraction was 50% of the total phosphorus (TP) whereas up to 7% of the TP was left after acid extractions. Negligible concentrations of heavy metals like Arsenic (As), cadmium (Cd), chromium (Cr) and lead (Pb) were found.