PubMed · 2026-06-30
An eight-year field experiment in southern Brazil found that repeatedly spreading chicken manure on farmland caused most heavy metals to stay within safe limits, but zinc built up steadily in the topsoil at higher application rates. The study highlights zinc as the element to watch most closely when using poultry litter as fertilizer.
After 8 years of annual poultry litter applications (up to 12 t/ha), arsenic, cadmium, chromium, copper, and nickel showed no significant accumulation in the 0-20 cm soil layer.
Zinc accumulated significantly in the surface 0-10 cm layer in a dose-dependent pattern, with higher application rates producing greater buildup.
All measured element concentrations remained below Brazilian regulatory thresholds throughout the study, but zinc's cumulative input represented the largest proportional increase relative to initial soil levels.