Poultry litter is widely used as fertilizer in soils and can be a relevant source of heavy metals for agricultural environments. In this study, poultry litter fertilization of long-term (< 1-30 years) was evaluated in tropical soils. Our main goal was to investigate the occurrence of temporal variation in the available fraction of heavy metals (Cu, Cr, Zn, Pb, Cd, and Mn) in soils, in addition to their environmental loads through new indexes for risk assessment. The highest mean concentrations in poultry litter were the following: 525 mg kg-1 for Mn, 146 mg kg-1 for Zn, and 94.4 mg kg-1 for Cu. For soils, concentrations were higher for the same heavy metals: Mn (906 mg kg-1), Zn (111 mg kg-1), and Cu (26.3 mg kg-1). Significant accumulation (p < 0.05) in fertilized soils was observed for Cu, Cr, and Zn. The high estimates of poultry litter input based on geological background (LIGB) for Cu, Cr, and Zn coincided with the accumulation observed in soils, confirming the effectiveness of the index. The risk of biogeochemical transfer based on fertilized soils (LIFS) decreased for Cu, Cr, and Zn between 10 and 30 years of soil fertilization. For Mn, a very high LIFS was estimated in all long-term fertilized soils. The proposed indices, based on heavy metal concentration, can be used in risk assessments to guide future studies that analyze other environmental matrices possibly impacted by manure and poultry litter fertilization.
Keywords: Agricultural soils; Environmental risk; Trace elements; Tropical soils.