Associate Professor University of Central Florida, Florida, United States
Abstract Submission: Accurate characterization of soil texture is critical to predicting saturated and unsaturated flows in phreatic and vadose zones. The objective of this research is to compare grain size analysis methods across a range of soil textures. Soil samples (5 replicates from depths of 0-10 cm, 10-20 cm and 20-30 cm) of varying sand, silt, and clay quantities were selected from 5 sites across Florida. Organic matter was removed through ignition in a muffle furnace and organic matter content was recorded. Remaining mineral fractions were characterized for grain size distribution using 1) a composite method of dry sieve and specific gravity testing using a hydrometer (SHM) and 2) a laser diffraction method (LDM). The soils were tested in a CILAS 1090 particle size analyzer using a ratio of 1 gram sediment to 40 mL of 5% sodium hexametaphosphate solution. Resultant particle size distributions varied across methods; however, the deviation was a function of soil type. The two methods aligned well for sandy soils while soil texture classification based on the USDA scale varied greatly among the two methods for soils with finer (loamy, silty) grain size distributions. The finer the particle size detected by the laser, the more difficult it became to draw comparisons between the methods as the USDA classifications and sand, silt, and clay percentages became more varied. Sandy soils contained 14% more sand with SHM than LDM, with an R2 value of 0.84. Loamy soils contained 67% more sand with SHM and a lower R2 value of 0.19.
