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Radial Trenching

Radial trenching with AirSpade is done to modify soil composition, improve aeration, and encourage root growth to moderate depths (typically 10”-12” or more), and is especially effective when trees have highly stratified or shallow depth of viable soil or anaerobic conditions. Additionally, this application can be useful in planting areas where minimal disturbance is desired.

Radial trenching is shown to encourage deep root growth far reaching from the trunk and between structural root leaders. An appropriate soil augmentation strategy is vital to each individual project. Because radial trenching is not as uniform as air tilling for soil augmentation, it can produce undesirable concentrations of nutrients if not properly considered. It’s therefore important to carefully select amendments that are compatible with existing soils, and it can be beneficial to perform air tilling in combination with radial trenching. For example, it may be preferable to augment soil within radial trenches with a higher percentage of porous inorganic materials (such as sand) to improve aeration and to then amend the top soil with a higher percentage of organic nutrients using the more uniform air tilling (or root invigoration) procedure. Alternatively, established trees that are struggling to survive in poor soils may benefit from a long-term strategy in which radial trenching is performed several times and over the course of several years to make more extensive improvements to a tree’s soil.

Radial trenching is preferably done throughout the dripline or beyond. Once the removal of turf and plant material is complete and the trench pattern is laid out (it may be helpful to paint guides on the ground), the operator can begin excavation. The operator will continuously move the AirSpade while holding the tool at a 30° to 45° angle to achieve the specified depth and working side to side to control the trench width. While digging a trench, plywood sheets are recommended to cover adjacent trenches to prevent refilling. The soil can then be collected to be replaced or amended, or it may be augmented in place. An AirSpade can be used in the soil replacement process to help blend the new and existing soil, and to fill pockets around tree roots.

Linear trenching is a variation of radial trenching in which an area is trenched in parallel rows rather than in a radial pattern. This is useful for working in planted beds or in areas with trees planted closely together. Another technique similar to radial trenching is called root trenching, in which select primary root leaders are deliberately uncovered rather than avoided. Root trenching is often used to train roots deep into the soil, under a paved surface, and into adjacent planting soils or to install a root barrier. 

Technical Applications Bulletin

To learn more about performing air-spading procedures, tree health care and preservation read the full article below.