Investigating the effect of animal manure on colloidal-facilitated phosphorus transport

Preferential flow via soil macropores can enhance phosphorus (P) loss in leachate. The application of animal manure can further exacerbate P losses in leachate in various forms. Limited work has been done to quantify colloidal-facilitated-P loss in leachate as a function of manure type. Therefore, the goal of this study was to determine the impact of three manure types, namely, poultry litter, swine lagoon effluent, and dairy manure, on P leaching in various forms using column-based rainfall simulation experiments. Intact-undisturbed soil columns were collected from a pasture field located in Alabama, USA. The overall experimental design included four treatments with two replications each (poultry litter (solid) at rate 1, poultry litter (solid) at rate 2, dairy manure (semi-solid), and swine lagoon effluent (liquid) and unamended control). The bromide breakthrough curves showed evidence of preferential flow. The flow-weighted mean total P concentrations for treatment columns ranged from 5.4 to 6 mg L⁻¹, 6.22 to 12.18 mg L⁻¹, 0.95 to 1.42 mg L⁻¹, and 0.29 to 1.1 mg L⁻¹ for columns treated with solid poultry litter at rate 1, solid poultry litter at rate 2, swine lagoon effluent, and dairy manure, respectively. Colloidal P accounted for 5 to 49 % of the total P leaching from the treatment columns. Therefore, the results of this study show that colloidal-facilitated migration of P can be significant and should be considered when elucidating P transport in agricultural systems fertilized with animal manure.