Soil characteristic data for the current study show that average clay
content increased by 26% (287 g kg−1) within the 20- to 30-cm depth
as compared to the horizon above it (227 g kg−1; n=6). Shallow rooted
grass and annual crop treatments did not show improvement in
number of pores (Fig. 2) and porosity (Fig. 3) below the 30 cm depth.
However, trees with more structurally stronger roots tend to develop
more roots below this depth zone. Visual observations for this study
show that the root distribution patterns of soybean and grass agree
with the findings of Myers et al. (2007) that root diameters decrease
below the claypan with tree roots developing larger diameter roots
creating larger pores. Changes in clay content within a profile and its
influence on root growth and genetics of plants may have caused
observed differences in all three porosities measured within the soil
profile.