Changes in Soil Phosphorus from Manure Application

Abstract

Manure and mineral fertilizer P sources vary in their contributions to soil P pools. We conducted incubation experiments to (i) assess temporal changes in soil P concentration for 84 d following application of KH2PO4 or manure (beef, dairy, poultry, or swine), and (ii) to evaluate interactive effects of P rate, P source, and background P level on soil P pools 90 d after P application. Changes in soil P over time were evaluated following the amendment of a coarse‐loamy, mixed, frigid Typic Haplorthod soil (pH 5.8) at a rate of 100 mg total P kg−1 Water soluble P (WSP), 0.01 M CaCl2–extractable P (CaCl2–P), and modified Morgan P (MMP) declined to <3 mg P kg−1 soil within 21 d of application, following an exponential decay function; P extracted by anion‐exchange membrane (AEMP) and Mehlich‐III (M3‐P) also declined rapidly and are attributed to the high level of exchangeable Al and Fe in this soil. Ninety days after application, all soil P pools exhibited linear increases in concentration for application rates up to 800 mg P kg−1 soil, regardless of P source. Phosphorus applied as KH2PO4 was more efficient at increasing CaCl2–P and M‐3P. Manure P sources generally had a greater effect on MMP, and poultry manure was more efficient than all other sources. Efficiency of P sources at increasing soil P concentration (b, slope of linear regression) varied from <1% for rapidly available P pools (CaCl2–P) to nearly 50% for more recalcitrant P (M3‐P). Efficiency also increased as background M3‐P increased from 150 to 750 mg kg−1 soil. The amount of CaCl2–extractable P increased rapidly when soil P saturation ([Mehlich III‐P]/[Mehlich‐III Al + Fe]) exceeded 0.25 mol mol−1 Manure and KH2PO4 contribute to different soil P pools, and these differences are magnified at high application rates and high background soil P levels.