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 (Erogrostis cuxvula)
was particularly insensitive to high bulk densities. The root
systems of switchgrass (Panicum virgatum), birdsfoot trefoil
(Lotus corniculatus), and sericea lespedeza (Lespedeza
cuneata) 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.
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