Water Retention by Core and Sieved Soil Samples

Mechanical analyses and water retention by core and sieved soil at -⅓ and −15 bar matric potentials were determined for samples from 26 sites ranging in texture from sand to clay. Objectives were to obtain a basis for identifying which soils may be influenced by deep tillage and profile modification with respect to water storage capacity and to determine the magnitude of errors possible when using sieved soils to establish field soil water contents. At -⅓ bar potential, cores retained more water than sieved soil when the water content was below 11%. The opposite occurred at higher water contents. At −15 bars potential, cores contained about 1 percentage point more water than sieved soils throughout the water content range encountered. These results show that treatments which thoroughly disrupt the natural soil structure may decrease and increase the storage capacity of coarse- and fine-textured soils, respectively. When expressed as a percent of the core water content, differences between core and sieved soil contents at -⅓ bar potential ranged from −40 to +25% at 5 and 40% core water contents, respectively. At −15 bars potential, the range was from −52 to −4% at 5 and 25% core water contents, respectively. These differences indicate caution should be used when using sieved soils to infer water retention by field soils, regardless of texture. This study suggests deep tillage and profile modification may decrease and increase water storage in coarse- and fine-textured soils, respectively. However, because of structural development, organic matter content, and possibly clay size and type, results for individual soils may differ from those indicated by the relationships established. To more accurately evaluate the possible effects of deep tillage and profile modification on water retention, the soil in question must be analyzed.