Abstract Modification in evaporation and its parameters, the drying coeffecient ( k), the soil boundary coefficient ( k b ) and the effective diffusivity ( D w ) by three mulches was investigated in a laboratory experiment. The mulches used were sand, zeolite and scoria, of which the scoria rock mulch is of particular interest. The methods of application of the mulches were surface and subsurface. Mulching, in general, reduced evaporation. Evaporation from surface mulch treatments was significantly less than that from subsurface mulches. Cumulative evaporation from surface mulch treatments of sand, scoria, and zeolite was respectively 16.6, 20.3, and 28.6% of the control. Surface mulches reduced k and the effective D w by an order of magnitude compared to the bare soil. The k b of surface mulch treatment by scoria and zeolite was 21 and 30%, respectively, of the control.