Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 3/27/2004
Publication Date: 3/27/2004
Citation: Chung, S.O., Sudduth, K.A., Motavalli, P.P., Kitchen, N.R. 2004. Relating on-the-go-soil strength data to cone index. American Society of Agricultural Engineers Mid-Central Conference. Paper No. MC04-205.
Interpretive Summary: Precision agriculture aims both to minimize costs and environmental damage caused by agricultural activities and to maximize crop yield and profitability, all based on information collected at within-field locations. Soil strength, or compaction, is a factor that can vary considerably within fields and can also greatly affect crop yields. Because of this, farmers need a quick and inexpensive way to measure compaction. To meet this need, we previously built an on-the-go sensor that can take measurements continuously while traveling across a field. In this research, we compared the data from our sensor to data from a cone penetrometer, the standard device currently used to measure compaction. Two kinds of comparisons were made ' one comparison was based on computer models describing the two different sensors, while the other comparison was based on experimental data collected with them. From the computer models, we found that the two devices should interact with the soil very similarly, and that measurements from the two devices should be strongly related. These findings were partially confirmed by experiments, but the relationships were not as strong as the computer models predicted, and were also more complex. The relationships we developed in this research were only for certain soil conditions. If additional research confirms the relationships over a wider range of conditions, it will mean that the many scientific findings from cone penetrometer research can also be readily applied to our sensor.
Technical Abstract: We developed a horizontally operating on-the-go soil strength profile sensor (SSPS) so that the within-field spatial variability in soil strength could be measured at multiple 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), similar to the cone index (CI, MPa) of a vertically operating cone penetrometer. This study was conducted to obtain theoretical and empirical relationships between PSSI and CI data. Comparison of mathematical models and a sensitivity analysis of model parameters provided patterns of CI and PSSI in different soil and operating conditions. Patterns for both of the soil strength indices were 1) linear for unit weight of soil, cohesion, adhesion, and operating depth, 2) exponential for internal friction and soil-tool friction angles, and 3) quadratic for operating speed. Simulated CI and PSSI data showed very strong linear relationships when only one of the parameters changed. In soil bin tests, linear relationships were found between CI and PSSI, and there were only slight increases in PSSI when operating speed increased from 0.5 m/s to 2.5 m/s. Field data showed that overall both CI and PSSI were greater with higher bulk density, lower soil electrical conductivity (EC, lower values generally indicate coarser soil texture), and lower soil moisture. Relationships were different when the data were divided into sub-groups by operating depth and EC range. In models estimating CI, the effects of PSSI and its interaction with other variables were relatively clear at 30-cm and 40-cm depths. CI prediction models with the highest R2 were also found at these depths. When operating depth was included in the regression model, coefficients of determination increased from 0.347 to 0.505 and from 0.499 to 0.518 for the two field test sites.