Field Measurement of Evaporation from Soil Shrinkage Cracks

Abstract

AbstractWeighing lysimetry was used to determine evaporative fluxes from a natural shrinkage crack and from an artificially induced soil shrinkage crack. Evaporation from the soil surface, except at the crack opening, was prevented by covering the lysimeter with plastic film. Evaporation rates from the natural and induced crack averaged about 0.6 mm/day computed on the basis of the surface area of the lysimeter. The horizontal soil water flux in the liquid phase to the crack wall was quite low, indicating that most of the measured evaporation resulted from vapor transport from some distance in the soil pores to the crack walls. Diurnal variations in evaporation rates were closely related to diurnal changes in vapor pressure deficit of the atmosphere above the soil surface. Evaporation rates from the natural/crack experiment were practically the same when the crack and soil surface were exposed to the atmosphere as when only the crack opening was exposed. Therefore, most evaporation from cracked, dry clay soil occurs because of the presence of shrinkage cracks. The results suggest a possibility for conserving water by partially filling the shrinkage cracks with dry soil or mulch to reduce evaporation. The low evaporation rates measured, however, make the feasibility of such a practice doubtful.