nEstablishing soil compaction thresholds for the M1A1 Abrams tank at Camp Minden, Louisiana

Soil compaction is a primary impediment to vegetation regeneration on military land used for M1A1 Abrams tank training. As such, there is a need to identify soil compaction thresholds and develop guidelines with which military range managers can determine appropriate timing and intensity of training exercises using the 63-ton M1A1 tank. A study was initiated at the Camp Minden Louisiana Training Site (CMTS) to develop guidelines which will allow for maximum utilization of the land resource with minimum degradation. The study was designed to evaluate soil moisture content and traffic rates as experimental variables using a replicated 3 x 3 x 3 factorial design with 3 soil ‘moisture ranges’ (\u3c 20%; 20 to 30%, and \u3e 30% water fraction by volume, wfv) and 3 ‘traffic load rates’ (3, 6, or 9 passes) on 5 m2 plots. Comparison of pre- and post-trafficked soil bulk density (BD), soil penetration resistance (PR), and soil-moisture retention characteristics (SMR) were used to evaluate the effects of soil moisture and traffic rates on relative compaction. Post-trafficked BD increased in all treatment combinations with root-limiting thresholds of 1.65 g/cm3 exceeded at the 20 cm depth in the Mid (20% to 30%) moisture range plots with as few as 6 passes and in the Hi (\u3e30%) moisture range plots with as few as 3 passes. SMR curve data indicate a reduction in total porosity from 0.44 to 0.38 cm3/cm3 in soil cores from Hi moisture treatment plots with a corresponding shift in pore size distribution toward a predominance of smaller pores across the range of pressures investigated to 12.5 bars. We conclude that training exercises are best when moisture contents for ‘silty’ and ‘loamy’ soils are at or below 20% on a volume basis. Furthermore, training exercises should be avoided at moisture contents above 30% to prevent root limiting compaction levels. Soil moisture levels exceeding the recommended thresholds commonly occur between December and April at CMTS annually. Suspending training maneuvers for this period is impractical. Therefore, we recommend range management plans include disking operations to loosen soil in tank trafficked areas when compaction levels exceed 1.65 g/cm3