Submitted to: Abstract of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 2000
Publication Date: August 5, 2000
Technical Abstract: Soil water content and matric potential are measured in the same sample in laboratory water retention studies. In field studies, water content has commonly been measured with neutron probes, and capillary pressure has been measured with tensiometers. Water content and capillary pressure are measured in different soil volumes and at different spatial scales in this case. This can potentially create differences in water retention data obtained in the field and in the laboratory. Our objective was to use a large database to compare field and laboratory water retention; 135 data sets were found in the UNSODA database and literature. Course-textured soils have the average difference between field and laboratory water contents close to zero. Fine-textured soils with sand contents less than 50% have field water contents substantially smaller than the laboratory water contents in the range of water contents from 0.45 to 0.60. A polynomial regression explains 70% of variability in field water contents as computed from the laboratory data. Fractal scaling of the bulk density can contribute to the observed "field-lab" differences in volumetric water contents. Pedotransfer functions (PTFs) built from the laboratory water retention data can overestimate available water content, and underestimate saturated hydraulic conductivity and sorptivity values. There is a need to include scale effects in PTFs.