The Effect of Moisture on Phosphorus Diffusion in Coal Mine Spoils

Phosphorus diffusion coefficients (D) have been measured as a function of water tension (ψ) and water content (θ) in topsoil and spoil samples from two coal mine sites in western North Dakota. For all four soils, the observed dependence of D upon ψ and θ can be well described by equations of the form D = Ae-aψ + B and D = K(θ – E)P + B. The results show that D is almost 0 for water contents below that held at 15 bars, and it increases rapidly as the water in excess of that held at 15 bars increases. For most of the measurements, D in the spoil materials is greater than in the topsoils for a given moisture tension.