SMALL INCREMENT ELECTRIC SOIL SAMPLER

Authors: Wuest, Stewart; SCHILLINGER, WILLIAM - WASHINGTON STATE UNIVERSI

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2008
Publication Date: 10/2/2008
Citation: Wuest, S.B., Schillinger, W.F. 2008. Small increment electric soil sampler. Soil Sci. Soc. Am. J. 72: 1554-1556

Interpretive Summary: Measurement of soil bulk density and volumetric water content in small depth increments is a tedious and time-consuming task, but very important in many research applications. We designed and tested an electric sampler to improve accuracy and decrease labor requirements. The new method works even in loose, dry soils. The sampler uses an electric linear actuator to push an intact soil core out of the sampling tube. The soil core is maintained in a vertical position and protected from fracturing by remaining inside the tube until sectioned with a cutting knife. Precise length increments and flat cuts are easily obtained. Compared to existing incremental sampling technology developed 30 yr ago for loose, dry soil conditions, the electric sampler had a two-fold reduction in sample variability. The electric sampler requires only 7 min to collect a 26-cm core and section it into 2-cm increments compared to 20 min per core with the older sampler.

Technical Abstract: Measurement of soil bulk density and volumetric water content in small (< 2 cm) depth increments is a tedious and time-consuming task. Most methods require compositing several subsamples to control measurement error, and few are feasible with loose, dry soils. We developed and tested a sampler that uses an electric linear actuator to push an intact soil core out of the sampling tube. The soil core is maintained in a vertical position and protected from fracturing by remaining inside the tube until sectioned with a cutting knife. Precise length increments and flat cuts are easily obtained, even in loose soils. Compared to existing incremental sampling technology developed 30 yr ago for loose, dry soil conditions, the electric sampler had a two-fold reduction in sample variability. The electric sampler requires only 7 min to collect a 26-cm core and section it into 2-cm increments compared to 20 min per core with the older sampler. Accurate measurement of near-surface soil bulk density and/or volumetric water content is critical for many investigations. Monitoring soil carbon and quantifying seed-zone environments are prime examples of this need, but assessment of plant nutrients, chemicals, and pollutants are other important topics. In addition, accurate near-surface volumetric measurements are needed to model heat, water, and air flow. Since bulk density fluctuates spatially and temporally, it is important to make multiple measurements over space and time. Many useful incremental soil samplers have been developed. Most work best when soil water content is high enough to produce low soil strength but not so wet that the soil adheres inside the sampling tube (Doran and Mielke, 1984; Elliott et al., 1999; Grossman and Reinsch, 2002). This poses a problem when research needs to be conducted under dry or changing conditions. Most sampling methods depend on the soil remaining as an intact core while it is laid horizontally and sectioned into depth increments. This is not possible under dry, loose conditions such as those found in the tilled mulch layer of summer- fallowed soils. Pikul et al. (1979) developed a tool capable of sampling loose soil in 1-cm increments. The device used a 5-cm-square steel tube that is driven vertically into the soil to capture the soil core. After removing the sampler with the soil core inside, thin metal blades are inserted horizontally through slots at each depth increment. The soil from each increment is then removed sequentially. This sampler has been used successfully in numerous field studies during the past 30 years. The new device described in this paper is capable of sampling loose, dry soil and incorporates principles from several previous methods, while having advantages in speed and accuracy.