Switchgrass Cultivar, Harvest Frequency, Fertilizer Source, and Irrigation Effects on Near-Surface Soil Properties in West-Central Arkansas

Switchgrass (Panicum virgatum L.) has been identified as a model bioenergy feedstock crop and is expected to become an important feedstock for future renewable fuel generation. Agronomic management combinations that maximize monoculture switchgrass yield are generally well understood; however, little is known about corresponding effects of differing switchgrass management combinations on near-surface soil properties. The objective of this research was to determine the residual near-surface soil property effects of three years (2008 to 2011) of consistent management combinations to maximize switchgrass biomass production, including cultivar (‘Alamo’ and ‘Cave-in-Rock’), harvest frequency (1-cut and 2-cut systems per year), fertilizer source (poultry litter and commercial fertilizer), and irrigation management (irrigated and non-irrigated). Effects on soil properties were assessed on a Leadvale silt loam (fine-silty, siliceous, semiactive, thermic, Typic Fragiudult) at the USDA-NRCS Booneville Plant Materials Center in Logan County by evaluating soil bulk density, total water stable aggregates (TWSA), soil pH and EC, Mehlich-3 extractable soil nutrients, root density, and surface infiltration. Irrigating switchgrass, which did not increase past biomass production, increased (p \u3e 0.01) soil bulk density in treatment combinations where poultry litter was applied (1.40 g cm-3) compared to non-irrigated treatment combinations (1.33 g cm-3). Total WSA concentration was greater (p \u3c 0.05) in ‘Alamo’ (0.91 g g-1) than ‘Cave-in-Rock’ (0.89 g g-1) treatment combinations when averaged over all other treatment factors. Root density was greater (p = 0.031) in irrigated (2.62 kg m-3) than in non-irrigated (1.65 kg m-3) treatments when averaged over all other treatment factors. Surface infiltration rate under unsaturated conditions was greater (p = 0.01) in the 1-cut (33 mm min-1) than 2-cut (23 mm min-1) harvest treatment combinations when averaged over all other treatment factors, while surface infiltration rate under saturated conditions did not differ among treatment combinations (p \u3e 0.05) and averaged 0.79 mm min-1. Results from this study indicate that management decisions to maximize switchgrass biomass production affect soil properties over relatively short periods of time and further research is needed to develop local best management practices to maximize yield while maintaining or improving soil quality