Trace metal uptake in forage systems receiving long-term applications of alum-treated or untreated poultry litter

Authors: Ashworth, Amanda; Moore, Philip

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2023
Publication Date: 2/24/2023
Citation: Ashworth, A.J., Moore Jr, P.A. 2023. Trace metal uptake in forage systems receiving long-term applications of alum-treated or untreated poultry litter. Crop Science. 63(3):1634–1645. https://doi.org/10.1002/csc2.20918.
DOI: https://doi.org/10.1002/csc2.20918

Interpretive Summary: Among the best cost-effective best management practices for minimizing nutrient losses to the air soil and water following poultry litter land applications is adding alum (aluminum sulfate) between bird flocks tin poultry houses. In addition to these environmental improvements, poultry in-house greenhouse gas emissions are reduced 42% when alum is applied, which results in improved bird weight gains, improved feed conversion, lower mortality, and lower propane use. For these reasons, over 40% of the broilers (meat chickens) in the USA are currently grown with alum each year. Heavy metal accumulation in poultry litter and subsequent plant uptake has received recent attention due to perceived environmental and animal feed concerns. Researchers set out to test the effects of four rates of alum-treated litter, untreated litter and, inorganic fertilizer, as well as an unfertilized control on forage yield, metal uptake, and soil accumulation over two decades. Trace metal (arsenic, copper, selenium, and zinc) concentrations in forage for all treatments were in the range considered normal or sufficient, hence, alum-treated litter did not cause any deficiencies or toxicities. Forage S and Zn concentrations were greater in plants fertilized with alum-treated than normal litter or inorganic fertilizers. During this 20 year study, forage yields with alum-treated and untreated litter were greater than inorganic nitrogen applied at the same total nitrogen rate. There were no differences in forage yields between the two litter types, except at the lowest litter rate, where fertilizing with alum-treated litter resulted in greater yields than untreated litter. Overall treating poultry litter with alum is a cost-effective best management practice that reduces nutrient losses, which improves air quality and poultry production and results in greater yields when low rates of litter are used. Alum also reduces heavy metal in runoff, thus improving water quality; and does not pose any issues with respect to metal phytotoxicity or toxicity to grazing animals.

Technical Abstract: Treating poultry litter with alum is a commonly used best management strategy for reducing ammonia (NH3) volatilization and phosphorus (P) runoff and leaching, however, little is known how this amendment affects trace metal availability and uptake by forages, as well as potential issues with phytotoxicity, toxicity to grazing animals, and overall yield. The objective of this study was to determine long-term effects of alum-treated poultry litter, untreated litter, ammonium nitrate, and an unfertilized control on trace metal (As, Cu, Se, and Zn) and S concentrations and uptake by tall fescue (Festuca arundinacea Schreb.), yield, as well as availability in soil. Greater (P<0.05) soil As and subsequent forage As uptake occurred with alum beyond the 6.72 Mg ha-1 rate, however, forage As concentrations were not affected by alum. Forage yields were greater with alum-treated and untreated litter than ammonium nitrate applied at the same N rate. Treating litter with alum generally did not improve tall fescue yields, except at the lowest litter rate (2.24 Mg ha-1). Alum-treatment of poultry litter has shown to be a cost-effective best management practice that reduces ammonia volatilization, which improves air quality and poultry production, while reducing P and heavy metal runoff and ultimately improving water quality. Given that trace metal and S concentrations in forages were all in the normal ranges, treating poultry litter with alum does not pose issues with respect to metal phytotoxicity and/or toxicity to grazing animals.