Long-term effects of poultry litter, alum-treated litter, and ammonium nitrate on aluminium availability in soils

Received for publication December 14, 2004. Research has shown that alum [Al2(SO4)3·14H2O] applications to poultry litter can greatly reduce phosphorus (P) runoff, as well as decrease ammonia (NH3) volatilization. However, the long-term effects of fertilizing with alum-treated litter are unknown. The objectives of this study were to evaluate the long-term effects of normal poultry litter, alum-treated litter, and ammonium nitrate (NH4NO3) on aluminum (Al) availability in soils, Al uptake by tall fescue (Festuca arundinacea Schreb.), and tall fescue yields. A long-term study was initiated in April of 1995. There were 13 treatments (unfertilized control, four rates of normal litter, four rates of alum-treated litter, and four rates of NH4NO3) in a randomized block design. All fertilizers were broadcast applied to 52 small plots (3.05 x 1.52 m) cropped to tall fescue annually in the spring. Litter application rates were 2.24, 4.49, 6.73, and 8.98 Mg ha¿1 (1, 2, 3, and 4 tons acre¿1); NH4NO3 rates were 65, 130, 195, and 260 kg N ha¿1 and were based on the amount of N applied with alum-treated litter. Soil pH, exchangeable Al (extracted with potassium chloride), Al uptake by fescue, and fescue yields were monitored periodically over time. Ammonium nitrate applications resulted in reductions in soil pH beginning in Year 3, causing exchangeable Al values to increase from less than 1 mg Al kg¿1 soil in Year 2 to over 100 mg Al kg¿1 soil in Year 7 for many of the NH4NO3 plots. In contrast, normal and alum-treated litter resulted in an increase in soil pH, which decreased exchangeable Al when compared to unfertilized controls. Severe yield reductions were observed with NH4NO3 beginning in Year 6, which were due to high levels of acidity and exchangeable Al. Aluminum uptake by forage and Al runoff from the plots were not affected by treatment. Fescue yields were highest with alum-treated litter (annual average = 7.36 Mg ha¿1), followed by normal litter (6.93 Mg ha¿1), NH4NO3 (6.16 Mg ha¿1), and the control (2.89 Mg ha¿1). These data indicate that poultry litter, particularly alum-treated litter, may be a more sustainable fertilizer than NH4NO3