Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/2/2004
Publication Date: 10/11/2004
Citation: Chung, S.O., Sudduth, K.A., Hummel, J.W., Motavalli, P.P., Kitchen, N.R. 2004. Empirical relationships between prismatic soil strength index and cone index. In: Proceedings 2004 International Commission of Agricultural Engineering (CIGR) International Conference, October 11-14, 2004, Beijing, China (CD-ROM).
Technical Abstract: Georeferenced measurements of soil strength can provide information useful for site-specific management. Because the conventional instrument for obtaining such measurements (i.e., cone penetrometer) provides only point data, we developed a horizontally operating on-the-go soil strength profile sensor (SSPS) that provides measurements at five depths up to 50 cm. Force divided by the base area of the sensing tip of the SSPS was defined as a prismatic soil strength index (PSSI, MPa), analogous to the cone index (CI, MPa) of a cone penetrometer. This study determined empirical relationships between PSSI and CI using data collected in an indoor soil bin at different operating speeds and depths, and from fields having variable soil texture, bulk density, and water content. In the soil bin tests, linear relationships were found between CI and PSSI at a single operating depth and speed. Effects of operating depth prevailed over speed effects. In field data, both CI and PSSI were generally greater at higher bulk density, lower apparent soil electrical conductivity (ECa, where lower values indicate coarser soil texture), and lower gravimetric soil water content. These patterns, however, were different when the data were classified into sub-groups by operating depth and ECa range. Linear regressions predicting CI as a function of PSSI and soil properties exhibited highest R**2 values at the 30-cm depth for a claypan soil site and at the 40-cm depth for a flood plain site. The effects of PSSI and its interactions with other variables were major factors in the models obtained at these depths. CI predictions were not good for data sub-groups with very large or small clay fractions (i.e., high ECa in the claypan site and low ECa in the flood plain site). When operating depth was added to the model, R**2 increased from 0.35 to 0.45 and from 0.51 to 0.53 for the claypan site and the flood plain site, respectively. Relationships between the two soil strength indices were not simple, as they were also dependent on soil properties and sensor operating depth. Even so, these CI-PSSI relationships will allow results obtained with the SSPS and other on-the-go soil strength sensors to be related to research studies where CI has been used to quantify soil strength.