ARS | Publication request: The Impact of Alum Additions on Organic P Transformations in Poultry Litter and Litter Amended Soil

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 21, 2007
Publication Date: March 5, 2008
Citation: Warren, J.G., Penn, C.J., Mcgrath, J.M., Sistani, K.R. 2008. The Impact of Alum Additions on Organic P Transformations in Poultry Litter and Litter Amended Soil. Journal of Environmental Quality. 37:469-476

Interpretive Summary: The treatment of poultry litter with alum (Al(SO4)3•18H2O) has been shown to be an affective method to reduce its soluble P content. This reduction in P solubility is beneficial because it decreases the potential for surface runoff P losses from agricultural lands receiving poultry litter. Generally the decrease in P solubility, which results from the addition of alum to poultry litter, is attributed to the formation of insoluble Al-phosphate compounds. However, no investigation of the influence of alum on organic P (Po) transformations in poultry litter is currently available. Therefore, a laboratory incubation was conducted in which poultry litter (with and without the addition of alum) was allowed to decompose for 93 days. Analysis of the organic P and inorganic P concentration is the litters indicated that organic P decreased by 73% in the non-treated litter, whereas in the alum-treated poultry litter its concentration increased by 34% due to litter dry weight loss. Extraction of the litter using various acidic and alkaline extractions showed that in the non-treated poultry litter the organic P was predominately in the form of acid soluble (1.0 M HCl) Po and in the alum-treated poultry litter, organic P was distributed between the alkaline (0.1 M NaOH) and acid soluble fractions. When applied to soils the alum-treated poultry litter treatment resulted in reduced concentrations of H2O soluble inorganic P and elevated concentrations of alkaline extractable organic P. These data demonstrate that the addition of alum to poultry litter not only results in the formation of insoluble Al-phosphate compounds but that it also inhibits the mineralization of organic P during litter decomposition and after soil application.

Technical Abstract: The treatment of poultry litter with alum (Al2(SO4)3•18H2O) has been shown to reduce P solubility. This decreased P solubility results in reduced risk of P in surface water runoff. Generally this decrease in P solubility is attributed to the formation of insoluble Al-P compounds after alum addition to poultry litter. However, no investigation of the influence of alum on organic P (Po) transformations in poultry litter is currently available. Therefore, a laboratory incubation was conducted in which poultry litter (with and without the addition of alum) was allowed to decompose for 93 days at 25 °C and an initial moisture content of 30%. Analysis of litters using liquid state 31P nuclear magnetic resonance showed that the phytic acid content of non-treated poultry litter (NTPL) declined by 73% whereas in the alum-treated poultry litter (ATPL) its concentration increased by 34% due to litter dry weight loss. Sequential fractionation of the litter sources showed that in the NTPL the Po was predominately in the form of acid soluble (1.0 M HCl) Po and in the ATPL, Po was distributed between the alkaline (0.1 M NaOH) and acid soluble fractions. When applied to soils the ATPL treatment resulted in reduced concentrations of H2O soluble inorganic P (Pi) and elevated concentrations of alkaline extractable Po. These data demonstrate that the addition of alum to poultry litter not only results in the formation of insoluble Al-Pi compounds but that it also inhibits the mineralization of Po.