Relating Soil Structure to Water Retention Using Multistripe Laser Triangulation Scanning.

Soil structure affects hydraulic properties, such as water retention, at or near saturation.  Because of the lack of quantitative methods for characterizing soil structure, it has been previously difficult to rigorously describe or generalize the relationship between structure and water retention.  A recent field-based 3-D scanning technology known as multistripe laser triangulation (MLT), however, has been shown in previous studies to capture interpedal pores larger than 0.03 mm in width.  These pores outline structural units in the soil. Our aim in this investigation was to relate MLT-quantified descriptions of soil structure to parameters of the water retention curve obtained using intact cores.  Multiple sites along a toposequence in northeastern Kansas were chosen to represent a range of soil structures and textures.  At each site, a pit was dug and profiles were cleaned using 1,1-diflourethane to remove artifacts from the excavated surface, leaving the natural soil face.  Profiles were left to dry for 2-3 days to reveal the dominant structures after which they were scanned using MLT.  An evaporative method was used on the intact soil cores to obtain water retention data from saturation to tensiometer cavitation.  Pressure plate extractors and a chilled-mirror dewpoint potentiameter were used to obtain water retention points from disaggregated soil material in order to define the drier end of the retention curve for each sample. Several water retention functions were fit to the data and the metrics obtained from the 3-D scans that quantify structure were related to parameters of these functions.  Relationships between the MLT-derived structural metrics and water retention curve parameters will be discussed.