The interactions between soil physical properties, particularly soil structure and bulk density, and the rooting of four herbaceous crops grown for biomass on three common Piedmont soil series were examined. The effect of these crops on soil properties over time was also studied. The rooting of the biomass crops studied seemed to be affected by soil physical factors on two of the three soils. Even though bulk density on all three soils (Appling, Cecil, and Davidson) appeared high enough to drastically limit rooting, such limitations were found only at the Appling sites and, to a much lesser extent, at the Cecil sites. Well-developed soil structure seemed to be instrumental in the success of the biomass crops on these dense Piedmont soils. All of the species studied had vigorous root systems in well-structured, high-density soils. Weeping lovegrass (<i>Erogrostis cuxvula</i>) was particularly insensitive to high bulk densities. The root systems of switchgrass (<i>Panicum virgatum</i>), birdsfoot trefoil (<i>Lotus corniculatus</i>), and sericea lespedeza (<i>Lespedeza cuneata</i>) were all heavily influenced by the high densities of the nearly structureless Appling soils; but lovegrass roots were quite prolific there. For this reason lovegrass should be considered first for biomass production on similar marginal soils. All soils had higher organic matter contents after four years of biomass production. Soil nutrient concentrations, particularly soil K, were also higher, especially under switchgrass. Soil Ca and Mg contents were higher under the two legumes than under the two grasses. / Master of Science