Coamendments to modify phosphorus extractability and nitrogen phosphorus ratio in feedlot manure and composted manure

A narrow nitrogen to phosphorus ratio (NIP) exists in animal manure, resulting in P high loading and pollution risks when land applications are made to meet IV demands of a crop. Nonhazardous mineral by-products potentially widen the effective NIP ratio in manure. We determined the effects of alum, caliche, and Class C fly ash on extractable P concentrations in stockpiled and composted cattle (Bos taurus) manure at rates of 0, 0.10, 0.25, and 0.50 kg kg(-1) manure. The mixtures were also added to Amarillo fine sandy loam (Aridic Paleustalf) and Pullman clay loam (Torrertic Paleustoll) at the rate of 22 Mg ha(-1). Caliche, alum, and fly ash reduced water-extractable P (WP) in stockpiled manure by 21, 60, and 85% and by 50, 83, and 93% in composted manure at the 0.1kg kg(-1) rate. Alum and fly ash also significantly reduced Bray-I P (BP) concentrations by 75 and 90% in stockpiled and composted manure, respectively, and >90% at higher rates. Fly ash also decreased Mehlich III-P (MP) concentrations, ranging from 50 to 98%. Mixing these amendments with feedlot manure widened the effective manure NIP ratio by a factor ranging from 1.5 to 18, Applying fly ash-treated stockpiled or composted manure reduced ail extractable P fractions from amended soils. Alum and caliche consistently reduced the WP fraction only. Coapplications of mineral and animal bg-products stabilized manure P where uncovered storage is unavoidable or widened its effective NIP ratio, allowing land application rates needed to fulfill plant N requirements without causing water quality impairments.