SPATIAL VARIABILITY OF EVAPORATION ALONG 2 TRANSECTS OF A BARE SOIL

Estimates of soil water evaporation are required for the assessment of soil water management practices. The purpose of this study was to investigate (i) the spatial and temporal changes in soil water evaporation along two transects in a bare soil, (ii) the spatial variability in soil properties, and (iii) the comparison of field-measured and simulated evaporation. The study was conducted on an Olton sandy clay loam soil (fine, mixed, thermic Aridic Paleustoll) at Lubbock, TX. Two 50-m transects were oriented in north-south and east-west directions with sampling positions marked at 1-m intervals. A 150-mm irrigation was applied and soil water evaporation was measured for the four succeeding days. Particle-size distribution and bulk density were determined from each sample after the last measurement. Semivariograms were calculated for each parameter along with the population statistics. Evaporation values were isotropic between transects for the first 3 d of measurement and did not exhibit any particular range for the semivariograms. We conclude that random samples can be taken to quantify soil water evaporation rates within this bare field. Population statistics for the bulk density revealed that the populations were random, normal distributions with no spatial structure, and for particle size the populations were either normal or log-normal. Values of soil water evaporation from the CONSERVB model were within one standard deviation of the mean of measured values when average soil hydraulic properties for the field were used. It is possible to use the average soil properties as input into a model for regional assessment of soil water evaporation rates.