Surface runoff contamination by chemicals initially incorporated below the soil surface

Rony Wallach*, Rina Shabtai

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


One method of reducing the contamination of overland flow by soil chemicals (e.g., nutrients, pesticides) is to reduce their concentration at the immediate soil surface. This can be done by incorporating the chemicals at lower depths, by either tilling the soil or by irrigating shortly after chemical application. A mathematical model designed to predict the runoff concentration of chemicals initially located at different depths below the soil surface is presented. The model accounts for transient water infiltration and convective‐dispersive solute transport in the soil, and also considers rate‐limited mass transfer through a laminar boundary layer at the soil surface/runoff water interface. Sorption‐desorption interactions between soil and chemicals are assumed to be subject to linear isotherms or to first‐order kinetics. The dissolved chemical concentrations at the soil surface and in the surface runoff were simulated for coarse and fine soils at different antecedent soil moistures and rainfall intensities. The simulation indicated that the initial depth of chemical incorporation below the soil surface is negatively correlated to the dissolved chemical concentration at the soil surface and in runoff water. A basic and characteristic difference between the chemical whose retention by the soil solids is expressed by an equilibrium model and the one whose retention is expressed by a kinetic model is soil surface concentration during water and chemical redistribution following the termination of rainfall and runoff. Contrary to the instantaneous equilibrium‐type chemicals, the dissolved concentration of the kinetic‐type chemicals increases sharply to its final value. For the coarser soil with higher saturated hydraulic conductivity, the relative chemical concentrations in surface runoff are lower than for the finer soil, when similar values of initial pressure head ψ0 and rainfall intensities (three times the saturated hydraulic conductivity of each soil) are used.

Original languageAmerican English
Pages (from-to)697-704
Number of pages8
JournalWater Resources Research
Issue number3
StatePublished - Mar 1993


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