, Volume 56, Issue 3, pp 253-261

Dissolved and particulate phosphorus in leachate from structured soil amended with fresh cattle faeces

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Abstract

Substantial transfer of phosphorus from land to aquatic environments has been observed in regions supporting intensive animal husbandry. We characterised leaching of P derived from fresh cattle faeces located at the surface of a structured clayey soil. Fresh cattle faeces were placed on top of an undisturbed column of structured soil (diam. and height 0.5 m) subjected to steady, saturated flow (1 mm h-1) with a synthetic rain solution. After 0.01 pore volumes (PV, 1PV = 46.5 1) or 2.5 h of flow the effluent concentrations of both dissolved and particulate P forms increased rapidly, and after 0.15 PV (37 h) a maximum of 12 mg P l-1 was observed for total P. This rapid, strong and permanent leaching of P from applied faeces was ascribed to preferential flow through continuous macropores. Dye tracing showed that especially earthworm burrows were active flow paths. Of the faeces derived P observed in the effluent, dissolved inorganic P (DIP, measured as molybdate reactive P) constituted the largest fraction (37%) followed by particulate organic P (POP, 33%) and particulate inorganic P (PIP, 22%) while dissolved organic P (DOP) accounted for the remaining 8%. Leaching of IP from faeces appeared to be greater than from inorganic sources. This may be ascribed to co-leaching of P complexating compounds, or compounds that compete with faeces derived P for sorption sites. When the flow regime was shifted from saturated to unsaturated conditions (after 5 days), DIP temporarily became undetectable in the effluent, and the concentration of PIP and POP decreased markedly, while DOP remained almost unchanged and became the main P fraction leached. Average effluent concentration of total P for the whole 12 day leaching period was 4.1 mg P l-1. This high concentration suggests well-drained soils with high animal densities to constitute future field research targets.