Direct gpr applications to agricultural investigations

Doolittle et al. (1998) used the State Soil Geographic (STATSGO; products/datasets/statsgo/) database to compare soil properties within the United States and Puerto

State Capitals

FIGURE 3.1 Ground-penetrating radar soil suitability map of the conterminous United States as presented by Doolittle et al. (2002).

State Capitals

FIGURE 3.1 Ground-penetrating radar soil suitability map of the conterminous United States as presented by Doolittle et al. (2002).

Rico as to their potential for GPR applications. This was an excellent step in assessing all the soils in the United States for the radar, even though it was done on a national scale. Some of the maps they created included saline and sodic soils, and the proportion of soils with less than 18 percent clay. A more detailed map was created by Doolittle et al. (2002) and is shown in Figure 3.1. On this map, notice that the Midwest United States, the dominant agricultural region in the United States, has a low potential for GPR use. Thus, research in using GPR for agricultural purposes has not developed as quickly as it has for environmental intentions. This point also was discussed by Collins (1992) when she pointed out that Mollisols and soils with mollic epipedons (principal soils in the Midwest) have a low potential for GPR. But even so, other geophysical instruments can be used to study soils where the radar has slight potential. Doolittle and Collins (1998) compared EM induction and GPR in areas of karst in Florida and Pennsylvania. They determined that GPR was the geophysical tool to use in Florida where the soil has low pH, low cation exchange capacity (CEC), and low base saturation in comparison to the soils in Pennsylvania which were characterized by relatively high pH, high CEC, and high base saturation. The soils studied in Pennsylvania were better suited for EM applications. Agricultural applications of GPR include investigations that have a direct influence on agricultural production and management. Agricultural production and management may be affected by a limited soil depth restricted by bedrock, hardpan, or a shallow water table. In these soils, plant roots are constrained in growing volume.

Also, agricultural production and management includes using soil (e.g., peatland) as fuel. Many countries (e.g., Ireland, Sweden, Canada, Finland) mine peatlands for the organic soil that can be burned and then have a restoration process to reestablish the land for future generations. Finnish peatlands are a very valuable resource for the wealth of the country. Thus, Hanninen (1992) compared traditional drilling field methods used in Finnish peatlands to determine organic matter thickness and properties to radar data. His conclusions were that GPR could be used to locate the interface between peat and the material below provided that there is a significant difference in moisture content; and various peat layer types and aquatic sediments could be identified by radar.

The list of literature that has had success with GPR includes the following:

• Mapping bedrock depth in a glaciated landscape in Maine (Collins et al., 1989)

• Microanalyses of soil and karst on the Chiefland Limestone Plain in Florida (Collins et al., 1990)

• High-resolution mapping of soil and rock stratigraphy (Davis and Annan, 1989)

• Interpretations of a fragipan in Idaho (Doolittle et al., 2000a)

• Improvement of interpretation of water table depths and groundwater flow patterns using predictive equations (Doolittle et al., 2000b)

• Determination of forest productivity on a loamy substrata glacial drift soil in Michigan (Farrish et al., 1990)

• Assessment of Bt horizons in sandy soils (Mokma et al., 1990a) and ortstein continuity in selected Michigan soils (Mokma et al., 1990b)

All of the above used GPR to determine a soil feature that would have a direct affect on agricultural production. But there are also what may be called "indirect" applications of GPR. An example would be the determination of volumetric water contents in soil with GPR (van Overmeeren et al., 1997). This is an increasing area of radar application, and this is what I mean by indirect applications of GPR to agricultural investigations.

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