Thermal property values of a central Iowa soil as functions of soil water content and bulk density or of soil air content

Authors: TONG, BING - Nanjing Tech University; KOOL, DILIA - Iowa State University; HEITMAN, JOSHUA - North Carolina State University; Sauer, Thomas; GAO, ZHIQIU - Chinese Academy Of Sciences; HORTON, ROBERT - Iowa State University

Submitted to: European Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2019
Publication Date: 6/17/2019
Citation: Tong, B., Kool, D., Heitman, J.L., Sauer, T.J., Gao, Z., Horton, R. 2019. Thermal property values of a central Iowa soil as functions of soil water content and bulk density or of soil air content. European Journal of Soil Science. 71(2):169-178. https://doi.org/10.1111/ejss.12856.
DOI: https://doi.org/10.1111/ejss.12856

Interpretive Summary: Soil properties change over time, especially following tillage. Soil is fluffed up by tillage and settles under its own weight and with rainfall. It is challenging to measure changes in soil physical properties after tillage because they occur over time and are not the same for all of the soil layers. The purpose of this study was to measure changes in soil bulk density and thermal properties with time following roto-tilling of a soil in central Iowa. Undisturbed soil cores were collected at several intervals after tillage and rainfall events and taken to the lab for tests. Thermal properties were measured for dry, moist, and wet soil conditions. The results showed that the soil gradually became more dense with time and rainfall and this change in density affected the way the soil conducted heat. These findings are important because they show that soil thermal properties change significantly following tillage so if you want to predict soil temperature accurately you will need to understand these changes. This research is of interest to scientists interested in improving predictions of soil temperature following tillage.

Technical Abstract: Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content (v) and bulk density (BD). Both v and BD change with time, particularly in recently tilled soils. The objective of this study is to measure soil thermal properties (volumetric heat capacity Cv, thermal diffusivity k, and thermal conductivity K) as functions of v and BD on undisturbed soil cores obtained at selected times following tillage. A till field site was rototilled to decrease the surface layer BD. Subsequent rainfalls increased BD. Undisturbed soil cores were collected for measurements of thermal properties at saturated, partially saturated, and oven-dry conditions. Generally, k and K increased with increasing BD at a given v, and the amount of increase followed the order of partially saturated > saturated > oven-dry. Property Cv increased as BD increased in oven-dry and partially saturated soils, while it decreased for saturated soil. Increasing BD generally led to increases in Cv, k and K at a given v, and K was more sensitive to BD than were Cv and k. Thermal property measurements were used to produce surfaces of Cv, k, and K versus v and BD. The surfaces represented the field condition over time including tillage and subsequent wetting and drying cycles. Soil thermal properties not only varied with v, but also with increasing BD. The results indicated that soil bulk density should be considered as a dynamic property instead of as a static property. Clearly, recently tilled field soil properties are quite dynamic.