Soil Properties Under Switchgrass Fertilized with Nitrogen Across a Toposequence in North Eastern South Dakota.

In the past few decades, bioenergy crops, especially switchgrass (Panicum virgatum L.), became of interest as a source of energy and renovating marginal soils. The aim of this study was to evaluate the impact of switchgrass managed for bioenergy production on soil properties across the topographic gradient in north eastern South Dakota. The experiment had three nitrogen rates (0, 50, and 100 kg N ha^-1) replicated four times. Soil samples were collected in June, 2015 across a toposequence encompassing all landscape positions (i.e., summit, shoulder, backslope, footslope, and toeslope). Soil physical and chemical properties (e.g., soil texture, bulk density, pH, EC, total carbon, soil organic carbon (SOC), soil inorganic carbon (SIC), plant available silicon (PASi), amorphous Si (ASi), available phosphorus (P) and total N) were determined. The results of this work showed that concentrations of SOC and ASi increased (from 12.4 to 13.8 g kg^-1) and (from 157 to 214 mg kg^-1), respectively, in the Ap horizon when the N rate increased from 0.0 to 100 kg N ha^-1. In contrast, other properties decreased, e.g., SIC (from 18.8 to 16.2 g kg^-1), available P (from 11 to 7.4 mg kg^-1), PASi (from 31.1 to 27.9 mg kg^-1), bulk density (from 1.84 to 1.74 Mg m^-3), and pH (from 7.85 to 7.74) when N rate increased from 0.0 to 100 kg N ha^-1. Within each N rate, soil properties across the toposequence also changed downslope, e.g., concentrations of SOC, PASi, ASi, available P, and total N increased from the summit towards the toeslope position.