Correcting laboratory-measured moisture retention data for gravels

Vadose zone soils in desert environments often contain a high gravel fraction (>2 mm size). Laboratory measurements of moisture retention are typically made on the fine fraction (<2 mm size); the measurements are then corrected for field conditions by accounting for the gravel fraction in the sample. A frequently used correction procedure for gravelly soils is tested. A total of 23 samples, containing gravel fractions up to 80% (by weight), were analyzed in the laboratory. Retention data on <2 mn size fraction were obtained and compared with measurements on bulk (soil and gravel) field samples. Results indicate that for the relatively wet moisture regime considered in this study, retention data for gravelly soils can be estimated reasonably well by correcting the pressure cell measurements for the field bulk density and the fraction of fines present in the field samples. Further work is needed an resting the correction procedure for the dry moisture regime.