No abstract

Adding aluminum sulfate or alum to poultry litter is a best management practice (BMP) that reduces ammonia emissions and P runoff and leaching, although its longterm 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 (NH 4 NO 3 ), 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 NH 4 NO 3 . 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, NH 4 NO 3 , 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 NH 4 NO 3 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.