Yield, Energy Production, and Nitrogen Loss Potential of Grain and Switchgrass Cropping Systems Compared Over Claypan Soil Landscapes.

A better understanding of production and production efficiency as soil-landscapes vary is needed for bioenergy crops like corn (Zea mays), soybean (Glycine max) and switchgrass (Panicum virgatum).  The objective of this research was to examine the impact of topsoil depth overtop a dominant argillic horizon [often called depth to claypan (DTC)] on bioenergy crop yield, net energy produced (NEP), and nitrogen (N) fertilizer loss potential. While it has been well documented that topsoil depth on these soils plays an important role in storing plant-available water for grain crop yield, it is not well known how this same soil property affects switchgrass yield, NEP, and N loss. Nitrogen loss for these crops when grown on poorly-drained claypan soils are not well quantified for abnormally wet growing seasons, such as was the case from 2008-10 for much of Missouri.  Plot research was initiated in 2009 in Columbia, MO with corn, soybean, and switchgrass grown on a range of DTC depths (0 to 50 cm). Corn was fertilized with 168 kg N/ha and switchgrass with 0 and 67.3 kg N/ha (starting in 2010).  Corn yield decreased as DTC decreased for 2009 and 2010 growing seasons. Plant N measurements demonstrated that corn yield loss was the result of increased N stress with decreasing DTC. DTC has little effect on soybean (2009 and 2010) or switchgrass (2010 only) yield. However, N management for switchgrass production was influenced by DTC for some management scenarios examined. With a push for renewable energy, an understanding of the ability of a marginal soil for producing energy is critical.  The significance of this research is that it helps to establish the capabilities of claypan soils for producing energy crops; in particular switchgrass, and establishes the need for site-specific N management strategies that can be targeted to landscape variations.