Phosphorus Leaching from Soil Cores from a Twenty‐Year Study Evaluating Alum Treatment of Poultry Litter

Adding alum to poultry litter is a best management practice used to stabilize P in less soluble forms, reducing nonpoint‐source P runoff. However, little research has been conducted on how alum additions to litter affect subsequent leaching of P from soil. The objective of this study was to evaluate the effects of alum‐treated versus untreated poultry litter on P leaching from soil cores receiving long‐term poultry litter applications. Two intact soil cores were taken from each of 52 plots in a long‐term study with 13 treatments: a control, four rates each of untreated and alum‐treated litter (2.24, 4.49, 6.72, and 8.96 Mg ha−1), and four rates of ammonium nitrate (65, 130, 195, and 260 kg N ha−1). One core from each plot received the same fertilizer as for the previous 20 yr, whereas the other was unfertilized in the study year, resulting in a total of 25 treatments. Cores were exposed to natural rainfall, and P leaching was measured for 1 yr. The average soluble reactive P concentrations in the leachate varied from 0.16 to 0.44 mg P L−1 in fertilized alum‐treated cores, whereas leachate from cores fertilized with untreated litter ranged from 0.40 to 2.64 mg P L−1. At the highest litter rate (8.96 Mg ha−1), alum reduced total dissolved P and total P concentrations in leachate by 83 and 80%, respectively, compared with untreated litter. These results indicate that alum additions to poultry litter significantly reduced soluble and total P fractions in leachate. Core Ideas This study used soil cores from a 20‐yr small plot study. Alum additions to poultry litter have a legacy effect on soil‐test P. Soils fertilized with alum had significantly lower Mehlich‐3 P values below 10 cm. Alum additions bind organic P in poultry litter and soil. Total P leachate losses were reduced by 86% with alum.