Abstract
Site-specific crop productivity is heavily influenced by the ability of soil to store water and nutrients while still permitting excess water to drain. One of the most promising practices to define spatial soil heterogeneity in terms of physical characteristics is the application of electrical conductivity/resistivity maps. The instruments used to map such soil characteristics use galvanic contact and capacitive coupling resistivity measurements as well as electromagnetic induction. Despite the type of instrument, the geometrical configuration between signal transmitting and receiving elements defines the shape of the depth response function. To assess vertical variation of soils from the surface, many modern instruments use multiple transmitter-receiver pairs to record electrical conductivity/resistivity signals applicable to different soil depths. Alternatively, vertical sounding methods can be used to measure a change in apparent soil electrical conductivity with the depth at a specific location. This paper examines the possibility for dynamic assessment of soil profiles using a surface galvanic contact resistivity scanning approach, with transmitting and receiving electrodes configured in an equatorial dipole-dipole array. An automated scanner system has been developed and tested in the agricultural field environment with different soil profiles. While operating in the field, the distance between current injecting and measuring pairs of rolling electrodes was varied continuously from 40 to 190 cm. The resulting scans were evaluated against 1-m deep soil profiles and that of an electromagnetic induction instrument at various depths.
Highlights
Information about soil quality and its variations is relevant for agriculture, archaeology, and environmental assessment
Spatial changes in soil electrical conductivity (ECa) have been linked to spatial soil heterogeneity [1,2,3,4]
An electrical motor automatically moves the electrodes through a range of spacing
Summary
Information about soil quality and its variations is relevant for agriculture, archaeology, and environmental assessment. Traditional methods for soil exploration are laborious and, not economical for high-resolution soil mapping. Proximal soil sensing is a new discipline that combines soil sensors and data analysis methods to obtain high resolution soil information at a reasonable cost. Sensors for apparent electrical conductivity (ECa) and its reciprocal apparent electrical resistivity (ERa) have been the most popular for proximal soil sensing. The ability of soil to conduct and accumulate an electrical charge has been linked with several physical and chemical soil properties. In non-saline, non-hydromorphic mineral soils, the particle size distribution (soil texture) in combination with related soil attributes is typically the most influential factor for spatial variation of soil ECa [5], as smaller particles (clay and fine silt) are related to higher ion concentrations (greater surface charge) and superior water storage (smaller pore size)
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