Chicken manure builds up zinc in soil after years of heavy use
de Mello D, Tagliari MM, Sierra-Garcia MA, Bermeo-Fúquene P, Zanatta JL
Soil Health
If you spread chicken manure on your vegetable garden every year, zinc is the one element that quietly accumulates in your topsoil over time, even when everything else stays safely within limits.
Farmers in Brazil have been using chicken manure to fertilize their fields for years, and researchers wanted to know whether harmful metals were building up in the soil. After eight years, most metals stayed at safe levels, but zinc was the exception: it accumulated in the top layer of soil whenever larger amounts of manure were applied. This means gardeners and farmers using poultry litter regularly should keep an eye on zinc levels over the long run, even if everything looks fine in the short term.
Key Findings
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.
chevron_right Technical Summary
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.
Abstract Preview
Original paper
Medium-term impacts of poultry litter application on potentially toxic elements in soil under subtropical conditions in southern Brazil.
Poultry litter is widely applied as an organic fertilizer, yet concerns remain regarding the cumulative input and potential accumulation of potentially toxic elements (PTEs) in agricultural soils. ...
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