Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2022
Publication Date: 6/25/2022
Citation: Ashworth, A.J., Moore Jr., P.A., Bacon, T., Martin, J.W., Anderson, K.R. 2022. Twenty-year phosphorus trends in forage systems receiving aluminum sulfate-treated poultry litter. Agronomy Journal. 114(4):2310-2319. https://doi.org/10.1002/agj2.21132.
Interpretive Summary: Two of the greatest environmental issues associated with poultry production are emissions and phosphorus (P) runoff and leaching from manure. Runoff P concentrations from pastures fertilized with poultry litter can be high, even when relatively low application rates are used. Therefore, grassland producers need sustainable management tools for utilizing this important nutrient source, while minimizing non-point source pollution in the largest land-use category in the USA (47% of all agricultural land). Researchers have found that applying aluminum sulfate or alum to poultry litter and manure greatly reduces litter nutrient losses to the air, soil, and water and set out to assess, in a twenty-year study, if reducing soluble P in poultry litter results in P from poultry litter being unavailable to plants. Results of this 20-yr study indicates that reducing P solubility with alum does not cause P deficiencies in forage and/or negatively affect forage yields. Consequently, treating poultry litter with alum is a best management tool for reducing non-point source P pollution in forage production systems.
Technical Abstract: Adding alum to poultry litter is a best management practice (BMP) that reduces ammonia (NH3) emissions and phosphorus (P) runoff and leaching, although its long-term impacts on forage growth and P uptake are largely unknown. The objective of this study was to determine if reducing soluble P in litter with alum would result in forage P deficiencies or reduce yields. A 20-yr study was conducted to determine effects of 13 treatments (unfertilized control and four rates of alum-treated litter, untreated litter and, NH4NO3) on tall fescue (Festuca arundinacea Schreb.) yield and P uptake. Phosphorus uptake increased as rates of litter increased for both litter sources but was greater (P<0.05) for untreated litter, perhaps owing to luxury P uptake due to high water-extractable P in soil. Over 20-years, both litter sources had greater P uptake than NH4NO3. Average annual yields by fertilizer source across rates were 6.92, 6.64, 5.10, and 3.38 Mg ha-1 for alum-treated litter, untreated litter, NH4NO3, and controls, respectively. Forage yields increased with litter application rate, but there was no difference due to litter source, whereas yields were 34% lower with NH4NO3 due to soil acidification and potential forage P deficiency (<0.2% P). Multiple regression indicated that tall fescue P uptake was affected by total P application rate and WEP, whereas yields were influenced by nitrogen rates, Mehlich III P levels, soil pH, and rainfall. These results indicate that treating litter with alum is a sustainable BMP for improving air and water quality, without negatively affecting forage production.