Changes in growth of two C4 grasses (Schizachyrium scoparium and Paspalum plicatulum) in monoculture and mixture: influence of soil depth

The growth of Schizachyrium scoparium (Michx.) Nash (little bluestem) and Paspalum plicatulum Michx. (brownseed paspalum), two C4 grasses, was examined in monoculture and in mixed culture in three soil depths. Effects of soil depth and competition were both significant. Growth of both species increased as soil depth increased from 30 to 180 cm in pot experiments. However, P. plicatulum dry mass increased approximately four times more than S. scoparium as soil depth increased. Schizachyrium scoparium dry mass was always greater in monoculture while P. plicatulum dry mass was always greater in mixture. Significant interspecific competition was not measured in the shallow soil treatment (30 cm) suggesting equal competition. Significant interspecific competition was measured in the deeper soil treatments (90 and 180 cm), and P. plicatulum dry mass was clearly greater in mixtures in the two deeper soils. Paspalum plicatulum does not appear to prevent the growth of S. scoparium roots in the deeper soil, but seems able to exploit deeper soil resources by proliferating roots at depths where S. scoparium roots do not seem capable of growth.