Elution of inorganic and organic phosphorus from surface applied organic amendments

Abstract

Understanding the effects of organic amendments on the movement of organic and inorganic phosphorus (P) in soils is important for effective P management in agricultural soils. Thus, the effects of beef cattle manure, hog manure and biosolids on the downward movement of organic (Porg) and inorganic (Pi) P in Lakeland and Osborne soils were investigated. The amendments were added to the soils at the rate of 0, 200, 400 and 800 kg P ha-1 by mixing with the top 1 cm of soil in a column. The column was eluted with 20 pore volumes (PV) of 0.01 M CaCl2. The amount of total P (PT), Porg and Pi in the effluent was determined. The concentrations of Porg and Pi in the effluent increased as the rate of amendment application increased. A greater percentage of PT was lost as Pi in the soils amended with hog manure and biosolids, while in the soil amended with beef cattle manure, Porg constituted a greater portion of the total P eluted. As much as 63% of total P eluted from the Lakeland soil at the highest rate of beef cattle manure was in the form of Porg. Lakeland soil retained more Pi than the Osborne soil due to its greater P retention capacity. Organic P was lost within the 2nd and the 4th PV in the two soils, which illustrated the ease of Porg movement through the soil. In conclusion, both organic and inorganic P can move through the soil in organically amended soils and the risk of losing organic P by leaching is greater in soils amended with high rates of beef cattle manure. Key words: Biosolids, hog manure, beef cattle manure, elution, organic phosphorus, inorganic phosphorus