ACCUMULATION OF WATER IN SOILS UNDER GRAVEL AND SAND MULCHES

Opportunities to influence the portion of the precipitation that percolates through the soil to aquifers lie primarily in the management of vegetation to control transpiration and of the surface to control infiltration and evaporation. Rates of percolation and recharge are of major interest to those concerned with the quantity and quality of water in our aquifers. Evaporative loss, precipitation, and water accumulation were measured on 0.9-m-long columns containing soil topped by sand and gravel mulches in the field for 388 d. Results show evaporation reductions due to gravel and sand mulches of differing thickness, color, and particle size on soil surfaces. These data show effects of mulch thickness, particle size, and color on the steady and transient components of evaporation and provide coefficients for equations to help predict effects of such mulches on evaporation and accumulation of water in soils and aquifers. Gravel mulches 5 cm thick resulted in accumulation of 80 to 85% of the annual precipitation.