Soil Resilience Index: Establishing Soil Compaction Thresholds for a Military Tank Training Facility.

Soil compaction is a primary impediment to natural regeneration of vegetation on military land used for heavy mechanized training. As such, there is a need to identify critical soil compaction thresholds and to develop a model with which range managers can determine appropriate timing and intensity of training exercises using the M1A1 Abrams Tank. A study was initiated at Camp Minden Louisiana (CML) to develop such a model which will allow for maximum utilization of the land resource with minimum degradation. The relative degree to which a given soil may be compacted is primarily a function of soil particle size distribution, mineralogy, organic matter content, soil moisture content, and applied force (number of tank traffic passes). The soils at the CML study site have relatively uniform particle size distribution, organic matter and mineralogy. As such, the study is designed to evaluate soil moisture content and traffic rates as “model” parameters using a replicated 3 x 3 factorial design with 3 soil moisture ranges (< 20%; 20 to 30%, and > 30% water fraction by volume, wfv) and 3 traffic load rates (3, 6, or 9 passes) on 5m² plots. Correlation of pre- and post-trafficked soil bulk density (BD) measurements at 20 and 50 cm depths are used to evaluate the effects of soil moisture and traffic rates on relative compaction. Root limiting soil compaction levels as reflected by bulk density measurements in excess of 1.58 g cm^-3 in these fine textured soils was greatest at soil moisture levels of 20 to 30% with an average increase of 7% and a BD of 1.64 g cm^-3 with only 6 passes necessary to achieve threshold compaction levels.