Impacts of nitrogen fertilization rate and landscape position on select soil properties in switchgrass field at four sites in the USA

Switchgrass (Panicum virgatum L.) has been recognized as a potential bioenergy feedstock due to its high yield potential and benefits to the environment. However, little is known about the impacts of nitrogen fertilization and landscape position on soil properties in switchgrass fields at multiple locations in the USA. The objective of this study was to assess the impacts of application of nitrogen fertilization rate (N rate; zero, 0; medium, 56; and high, 112 kg ha−1) and landscape position (shoulder, backslope, and footslope) on soil pH, electrical conductivity (EC), soil organic carbon (SOC), total nitrogen (TN), nitrate-N (NO3−-N), and ammonium-N (NH4+-N). This experiment was established in 2008 at four sites in Oklahoma (OK), South Dakota (SD), New York (NY), and Virginia (VA). Data showed that the N rate significantly increased NO3−-N for the 0–5 and 5–15 cm depths at the SD, NY, and VA sites. Compared with the zero N rate, the high N rate averagely increased NO3−-N by 75.7% for the two depths and three sites. The SOC and TN increased with the increase in N rate at most of the depths. The landscape position significantly reduced soil pH and increased EC, SOC, TN, NO3−-N, and NH4+-N at the footslope compared with the shoulder and backslope positions in most depths at the SD site (no position data at the NY and VA sites). The pH generally increased and the SOC, TN, and NO3−-N reduced with the increase in soil depth. These findings indicate that switchgrass production has the potential to improve or maintain soils in the USA. •N rate significantly increased soil NO3−-N at the SD, NY, and VA sites.•There was an increasing trend in SOC and TN with N rate at the four sites.•Position significantly impacted soil properties at SD site but not for OK site.•Lower pH and higher EC, SOC, TN, and NO3−-N at footslope than shoulder at SD.•pH increased and SOC, TN, and NO3−-N reduced with increasing soil depth.