Twenty‐year phosphorus trends in forage systems receiving aluminum sulfate‐treated poultry litter

Abstract

AbstractAdding aluminum sulfate or alum to poultry litter is a best management practice (BMP) that reduces ammonia emissions and P runoff and leaching, although its long‐term effects on forage growth and P uptake are largely unknown. The objective 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 four rates of alum‐treated litter, untreated litter, and ammonium nitrate (NH4NO3), as well as an unfertilized control on tall fescue (Festuca arundinacea Schreb.) yield and P uptake. Phosphorus uptake increased as litter rates increased for both sources but was greater (P ≤ .05) for untreated litter, likely owing to high water‐extractable P in soil. Over 20 yr, 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 the control, 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 forage P deficiency (≤0.2% P). Multiple regression indicated tall fescue P uptake was affected by total P application rate and water‐extractable phosphorus (WEP), whereas yields were influenced by N rates, Mehlich III P levels, soil pH, and precipitation. These results indicate that amending soils with alum‐treated litter does not adversely affect tall fescue yields or P utilization, therefore alum is a sustainable BMP in pasture systems.