Surveying the Near-Surface Fibrous Roots of The Orange Tree With 3-D GPR
Freeland, R. S.  2016.  Applied Engineering in Agriculture,  32(2): 145-153.

The orange tree [ (L.) Osbeck] has delicate fibrous roots whose purpose is to absorb soil moisture and nutrients. They are provisioned by larger structure roots, which from the tree extend outward. The majority of the fibrous roots lie underneath the tree‘s canopy in a matted layer just beneath the surface. In a commercial grove, approximately two-thirds of the root mass remains within the tree row, whereas the remainder extends outward toward both alleyways. A robust fibrous citrus root system will enhance the tree‘s ability to withstand soil-borne disease and pests, and endure exposure to cold and drought. A sparse, non-vibrant fibrous citrus root system is an indicator of tree stress. Total citrus root mass along with canopy size are directly related to fruit yield. Ground-penetrating radar (GPR) was evaluated in this case study for surveying fibrous citrus roots on the major citrus-producing Ridge and Flatwood soils of Florida. As the very small fibrous roots cannot be resolved individually using traditional GPR root-detection methods, a 2500-MHz antenna was used to visualize the spatial distribution and uniformity of the fibrous root mat.