Impact of M1A1 main battle tank disturbance on soil quality, invertebrates, and vegetation characteristics

Military training commonly results in land degradation, but protocols for assessing and predicting long-term environmental impact are lacking. An ability to assess the impact of repeated disturbance and subsequent recovery is needed to balance training requirements against environmental quality. To develop methodology for assessing soil quality, a study evaluating disturbance resulting from tank maneuvers was initiated on Fort Riley Military Installation, Kansas. The objectives were to identify and quantify soil-quality indicators on two soil types exposed to controlled tank traffic. We examined physical, chemical, and biotic indicators after treatments were applied during wet and dry soil conditions. A randomized complete-block design, with three blocks per soil type and three treatments per block, was used. Treatments consisted of disturbance created by a 63-ton M1A1 tank making five passes in a figure-8 pattern during either dry or wet soil conditions. The M1A1 was operated at a speed of approximately 8 km/h. Control plots received no tank traffic. Soil-quality indicators evaluated were soil compaction, soil penetration resistance, rut depth, soil bulk density, soil texture, soil chemical composition, plant biomass, soil microbial diversity, and nematode and earthworm taxa. Soil-quality indicators were sampled within one week after tank disturbance. Preliminary data indicate soil-texture-dependent treatment effects (p  0.05) for bulk density and porosity. Bulk density increased and porosity decreased on trafficked areas, in the silt loam soil, but showed no change in the silty clay loam soil. Disturbance during wet soil conditions raised penetrometer resistance and gravimetric water content more than disturbance during dry soil conditions (p  0.05). A significant difference in disturbance was measured between the outside and inside portion of the same track (p  0.01 and 0.001, respectively). The outside track caused the greatest amount of disturbance, as measured by the height of the disturbed soil ridge above the track bed. Tank disturbance significantly reduced total vegetative biomass (p  0.05) compared with that of un-trafficked areas. Disturbance under wet soil conditions significantly reduced grass biomass (p = 0.040), whereas disturbance under dry soil conditions significantly reduced forb biomass (p = 0.0247) compared to un-trafficked areas. Total earthworm abundance (p = 0.011) was reduced by 82% when disturbance occurred during wet soil conditions regardless of soil type.