Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/20/1998
Publication Date: N/A
Interpretive Summary: Soil electrical conductivity (EC) is influenced by a number of factors, including soil moisture, clay content, and salinity. Because of this, spatial measurements of conductivity can, when properly calibrated, provide indicators of a number of soil parameters important in site-specific crop management, or precision agriculture. In our work on claypan soils, we have found EC to be strongly correlated with the depth of topsoil above th claypan horizon. Since the claypan restricts water movement and root growth, topsoil depth is closely related to crop yields, especially in the water-limited growing seasons which are common in the claypan soil area. Two types of EC sensors usable in precision agriculture are commercially available. The Geonics EM38 is a non-contact sensor which measures EC to a depth of approximately 1.5 m through the principle of electromagnetic induction. The Veris 3100, a newer product, uses coulters in contact with the soil to provide two simultaneous EC measurements to depths of approximately 0.3 m and 0.9 m. We obtained EC measurements over a number of claypan soil fields using both these instruments, and found that they gave similar, but not identical results. In some situations, the EM38 information was more useful, while in other situations the Veris readings were better suited to determine soil variability. The results of this research will benefit users of EC instruments, giving them a better understanding of the advantages and limitations of each type. The results will also benefit scientists and extension personnel, who may need to understand the differences between the instruments for research or demonstration purposes.
Technical Abstract: Soil electrical conductivity (EC) sensing provides a means for rapidly mapping variations in soil properties such as salinity, moisture, and clay content. On claypan soils, EC measurements are related to topsoil depth above the claypan horizon, an important factor in spatial crop productivity differences on these soils. Soil EC data obtained with a noncontact sensor rbased on electromagnetic induction principles were compared with data from a direct contact, coulter-based sensor. Differences in EC readings were attributed to differences in sensing depth between the sensors and operating modes. The electromagnetic induction sensor generally provided better estimates of topsoil depth and correlations to crop productivity over the full range of topsoil depths encountered (up to 150 cm). However, the coulter-based sensor performed well at shallower topsoil depths (up to 90 cm), and would also be useful for investigating soil differences in precision agriculture practice.