The Effect of Soil Surface Conditions on Evaporation of Soil Water 1

A laboratory study investigating the comparative effectiveness of a dust, a ground corncob and a gravel mulch in inhibiting the evaporation of soil water from prepared 15-inch long soil cores 3 inches in diameter under various conditions of radiation (0, 200, or 450 ft-c.) and air movement (0.5 and 7.5 feet per second) showed the gravel mulch to be more effective than either a dust or a ground corncob mulch. The dust mulch proved to be the least effective. For example, the rate of loss from the mulched cores under conditions of 450 ft-c. of radiation and air movement of 7.5 feet per second was 0.089, 0.146, and 0.170 g. per hour for the gravel, the corncob and the dust mulch, respectively. It was also observed that the rate of evaporation from the cores increased with both radiation and air movement levels. By the end of 600 hours unmulched cores had lost 1.25 to 5 times as much water as had mulched cores. A concurrent study of the soil moisture distribution that develops with depth as evaporation of soil water proceeds was conducted. The study indicated that the soil moisture distribution in the mulched cores and for the 6- to 15-inch depth of unmulched cores remained essentially constant with depth.