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The release of soil phosphorus to runoff in relation to the kinetics of desorption

Sharpley, A.N., Ahuja, L.R., Menzel, R.G.
Journal of environmental quality 1981 v.10 no.3 pp. 386
phosphorus, kinetics, desorption, soil erosion, water pollution, soil nutrients, rainfall simulation, agricultural soils, agricultural runoff, hydrologic models, soil erosion models, linear models, water solubility, rain intensity, phosphates, soil aggregation, pollution load
The release of P from surface soil to runoff water under simulated rainfall conditions was investigated for five soils at several rates of fertilizer P application. A simplified kinetic model proposed earlier, describing the desorption of soil P, adequately described both the concentration of soluble P in runoff during an event and mean values for successive events. During an event the logarithm of soluble P concentration decreased linearly as the logarithm of time increased. Mean soluble P concentrations of individual runoff events increased linearly with amount of desorbable P in the surface soil (top 0.5 cm), while the effect of increased rain intensity on concentrations could be explained by a power function related to water/soil ratio. The average depth of runoff-surface soil interaction calculated from the data using the kinetic model ranged from 1.5 to 3.0 mm for the five soils, and was significantly related to degree of soil aggregation. These depths agreed closely with those determined using 32P as a tracer in earlier studies. The depth of interaction increased with increase in soil slope, kinetic energy of the raindrops, and, to a lesser extent, rainfall intensity. The use of the kinetic model would improve modeling of soluble P loading in runoff.