Nitrogen Cycling in Switchgrass Varieties

The Science

Determine differences in nitrogen (N) acquisition and conservation between switchgrass varieties to optimize growth with the least amount of fertilizer usage by measuring N fixation, N mineralization, and N translocation along with soil moisture and N content in switchgrass varieties from upland and lowland ecotypes.

The Impact

  • N fixation was highly variable among switchgrass varieties, but in general lowland ecotypes had significantly higher yields, N translocation, and root N fixation, with lower soil N fixation than upland ecotypes.
  • N cycling differences might be due to root and soil microbiome differences in switchgrass varieties.
  • Many switchgrass varieties can achieve high yield without N additions, decreasing the economic and environmental cost of growing this bioenergy crop.


In nitrogen (N)-limited terrestrial ecosystems, plants employ various strategies to acquire and conserve N, including translocation of N in perennial tissues and stimulation of N fixation in roots and soils. Switchgrass (Panicum virgatum L.) is a genotypically and phenotypically diverse perennial grass with two distinct ecotypes (lowland and upland) and numerous genotypes. It grows well in low-N soils, likely because of its ability to translocate N and to associate with N-fixing microbes, but little is known about variation in these traits among cultivars or even ecotypes. We measured N translocation, N fixation potential in roots and soils, soil net N mineralization, soil net nitrification, and biomass yields in 12 switchgrass cultivars grown in a replicated block experiment in southwestern Michigan, USA. Lowland cultivars had higher yields, rates of N translocation, soil net N mineralization, and N fixation potentials on washed, non-sterile roots, while upland cultivars exhibited higher N fixation potentials in root-free soil.


Roley, S.S., T. C. Ulbrich, and G. P. Robertson. 2020. “Nitrogen Fixation and Resorption Efficiency Differences Among Twelve Upland and Lowland Switchgrass Cultivars,” Phytobiomes 116, 071802. DOI:10.1094/PBIOMES-11-19-0064-FI.