Modified centroid for estimating sand, silt, and clay from soil texture class

TitleModified centroid for estimating sand, silt, and clay from soil texture class
Publication TypeJournal Article
Year of Publication2017
AuthorsLevi M
JournalSoil Science Society of America Journal
Start Page578
Date Published06/2017
ARIS Log Number333989

Models that require inputs of soil particle size commonly use soil texture class for input; however, texture classes do not represent the continuum of soil size fractions. Soil texture class and clay percentage are collected as a standard practice for many land management agencies (e.g., NRCS, BLM, FAO) and clay content is frequently estimated with acceptable accuracy (±5%). When clay and texture class is known, sand and silt can be constrained to a narrow range that may differ from the geometric centroid of a given texture class (gcent). I tested the concept of a modified centroid approach (mcent) using 75,736 soil samples from the National Cooperative Soil Survey pedon database that also had measured hydraulic soil properties. Comparisons were made using the Rosetta pedotransfer function (PTF) to test modeled values from gcent, mcent, and measured data in comparison to measured values of water content at field capacity ('330) wilting point ('15000,). The mcent approach produced a continuous distribution of values for sand and silt whereas gcent produced a stair-step pattern for each of the 12 texture classes. Rosetta underestimated water content. Unbiased root mean square error was smaller for mcent than gcent for seven and ten of the 12 soil texture classes for '330 and '15000, respectively. Results support the practice of collecting field estimates of clay percentage along with texture class to expand the use of soil profile data for both spatial and non-spatial modeling of soil processes that will advance our understanding of soil contributions to ecosystem function.