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

Abstract

AbstractTreating poultry litter with alum (Al2[SO4]3·14H2O) is a commonly used best management strategy for reducing ammonia (NH3) volatilization and phosphorus (P) runoff and leaching. However, little is known about 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 longitudinal 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 over 20 years. Greater (p < 0.05) Mehlich‐3 extractable 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 litters than with 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 been 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.