Soil Organic Carbon and Nitrogen Dynamics in Switchgrass Seeded to a Marginally Yielding Cropland in South Dakota.

Switchgrass (Panicum virgatum L.), as a biofuel feedstock, potential ecological impacts have been assessed under different environmental conditions. However, little is known about the information of integrated analysis of soil organic carbon (SOC), nitrogen (N) fertilizer, soil nitrate (NO₃^-), soil nitrous oxide (N₂O) emissions, and NO₃^- leaching in South Dakota. The objective was to explore SOC and N dynamics for 2009 through 2015 in switchgrass seeded to a marginally yielding cropland based on treatments of N fertilization rate (N rate) (low, 0; medium, 56; high, 112 kg N ha^-1) and landscape position (shoulder, backslope, and footslope). Our findings indicated that N rate did not impact SOC at all five depths from 2009 to 2013. The SOC at the 0- to 5-cm depth had an increasing trend over the five years. N rate impacted soil NO₃^- (0-5 cm depth) and soil surface N₂O fluxes but did not impact NO₃^- leaching after five years of continuous growing switchgrass. Medium N (56 kg N ha^-1) was the optimal rate for increasing the biomass yield with reduced environmental problems. Landscape position impacted the SOC and N dynamics. At the footslope position, there was higher SOC, soil NO₃^-, soil NO₃^- leaching, and N₂O fluxes than the other landscape positions. Growing switchgrass on marginally yielding croplands can improve SOC, store soil N, reduce N losses via leaching, and mitigate N₂O emissions from soils to the atmosphere over the observed years.