Impact of Bioenergy Grass Production on North Carolina Piedmont Soil Properties.

Bioenergy grasses are potential alternatives to traditional row crop and pasture/hay systems in the Piedmont region of North Carolina; but there are limited data from the area about the effect of annual/perennial cropping systems on soil resources. The objective of this project was to evaluate the impact of land conversion to bioenergy crops on soil properties and water availability. The research was conducted at a research farm site with no-till practices in the upper piedmont region of NC. Five cropping systems were included: switchgrass, giant miscanthus, biomass sorghum, fescue hay and corn/wheat/soybean rotation. Biomass (and grain) yield, soil nutrient reserves, crop water usage and crop light use efficiency were evaluated during a 3-year conversion period. Perennial crops were established in spring 2012; annual crops were planted in April or May each year since 2012. Weather parameters (rainfall, potential evapotranspiration, etc.) were monitored by an onsite weather station. Soil nutrient reserves among different cropping systems were compared after 3 years of crop establishment, in soil samples collected at multiple depths (0-20, 20-40, 40-60, 60-90, 90-120cm). Crop water requirements were estimated by volumetric water content measurements coupled with potential evapotranspiration. For each cropping system, photo synthetically active radiation (PAR) was measured at ground level for comparison to above canopy PAR so that light use efficiency of these cropping systems could be determined.

Biomass sorghum had an average yield of 23.8 Mg ha^-1 across 3 years.  When maturity was reached in 2014, giant miscanthus and switchgrass out-yielded fescue hay (9.8 Mg ha^-1) by 120% and 54%, respectively. In 0-20 cm soil depth, the soil acidity of swithgrass and miscanthus plots was significantly (at α=0.05 level) lower than that in fescue plots. Additional data will be discussed.