Nitrogen Fertilization Rate and Landscape Positions Impacts on Root Growth Parameters of Switchgrass.

Switchgrass (Panicum virgatum L.) has been extensively studied for its value as a forage, conservation, and bioenergy crop, and soil carbon sequestration. The present study was conducted near Bristol in South Dakota, USA to evaluate the nitrogen (N) fertilizer and landscape positions impacts on switchgrass root growth parameters. The specific objective was to assess the impact of nitrogen (N) and landscape positions on root length density, surface area of roots, root C and N of switchgrass. The experimental layout was a randomized block experiment that contained three N levels (low, 0 kg N ha^-1 and high, 112 kg N ha^-1). The experiment was repeated at shoulder, backslope, and toeslope landscape positions. The soil at the site was a Nutley-Sinai (silty clay, mixed, Chromic Hapluderts). Switchgrass was planted in 2009 on a marginal land previously used for croplands, and root sampling was done after 4 years of planting (2013). Soil cores from 0-100 cm depth were collected from every treatment and each core was subdivided into five sections (0-15, 15-30, 30-45, 45-60, and 60-100 cm). Roots were separated from soil for these individual depth sections, and root physical properties (length, area, volume, and density) for each depth were measured using WinRHIZO software. Soil properties (such as soil organic and inorganic carbon, bulk density, and N) were related to root growth. Results showed that toe slope areas had higher soil organic carbon (SOC) and lower bulk density values than eroded shoulder areas. The N rates did not significantly influence soil properties. Data collected from this study imply that establishment of switchgrass on marginal lands improve soil carbon accumulation and root parameters which enhance soil quality thus improving the switchgrass biomass production and environmental quality of the landscape.