Sustainable biomass feedstock production systems involve biomass generation from non-agricultural or marginal lands with minimal external inputs. Switch grass based alley cropping systems have been proposed as biomass feedstock crop systems in marginal lands. In many areas in the midwest United States, shallow soils above theargillic horizon (claypansoil or often called depth to claypan(DTC)) are susceptible to flooding and drought and thus hinder high economic returns from conventional agricultural production. The main purpose of this research was to assess differences between corn and switchgrass photosynthetic potential as influenced by the DTC. Research was initiated in 2009 in Columbia, MO on 160 plots with corn, soybean, and switchgrass grown on a range of DTC (0 to 80 cm). Biomass data from 2009 to present have revealed that corn yield was sensitive to DTC with greater yield as DTC increased (p=<0.06) while switchgrass yieldproved to be insensitive to DTCfor all years except in 2012. To understand, the fundamental mechanism driving this trend, we used a portable photosynthesis measurement unit (LiCor 6400) to measure the light response curves for corn and switchgrass at three different soil depths – shallow (2 cm), medium (22 cm), and deep (42 cm). Results suggest that soil depth was more important for corn to maintain a high rate of photosynthesis while switchgrass was able to maintain photosynthesis in a more uniform rate irrespective of soil depth. The significance of this research is that it establishes that switchgrass can be used as an alternative bioenergy crop in marginal lands degraded due to erosion such as commonly found in side-slope landscape positions of claypan soils.