Near-term effects of perennial grasses on soil carbon and nitrogen in eastern Nebraska

Authors: Ramirez, Salvador; Schmer, Marty; Jin, Virginia; Mitchell, Robert - Rob; ESKRIDGE, KENT - University Of Nebraska

Submitted to: Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2023
Publication Date: 5/6/2023
Citation: Ramirez II, S., Schmer, M.R., Jin, V.L., Mitchell, R., Eskridge, K. 2023. Near-term effects of perennial grasses on soil carbon and nitrogen in eastern Nebraska. Environments. 10(5):80. https://doi.org/10.3390/environments10050080.
DOI: https://doi.org/10.3390/environments10050080

Interpretive Summary: Perennial warm-season grass such as switchgrass and big bluestem can be used to produce biofuels. Compared to corn production, the production of switchgrass may emit less carbon (and other planet warming greenhouse gasses) into the atmosphere by storing more carbon in soil. Warm-season grasses can be grown alone in monoculture or in mixtures with other warm-season grasses, but the benefits of growing them in mixtures remains unclear. We compared the aboveground biomass of two perennial warm-season grasses and one low-diversity mixture of warm-season grasses, as well as the soil organic carbon under the warm-season grasses compared to adjacent corn plots. We found that the yield of warm-season grasses was greater when grown in a low-diversity mixture compared to the monocultures of switchgrass and big bluestem, even through some growing seasons with below average precipitation. The significance of this finding is that increasing grass diversity (i.e., the low diversity mix) may increase their ability to adapt to climate variability. We also found that the amount of organic carbon in the soil was greater under the low diversity mixture, but only compared to one of the grass monocultures. We also found no differences when comparing soil organic carbon under the warm-season grasses and corn. This could be due to the duration of this study (five years) or the fact that these soils already had a high amount of soil organic carbon compared to other regional studies. The significance of this finding is that we must continue to monitor the effect of both corn and perennial grasses on soil organic carbon in order to effectively determine which systems (i.e., corn systems and perennial grass systems) produce enough biomass to make bioenergy while minimally emitting greenhouse gases.

Technical Abstract: Incorporating native perennial grasses adjacent to annual row crop systems managed on mar-ginal lands can increase system resiliency by diversifying food and energy production. Here, we evaluated (1) soil organic C (SOC) and total N stocks (TN) under warm-season grass (WSG) monocultures and a low diversity mixture compared to an adjacent no-till continuous-corn system, and (2) WSG total above ground biomass (AGB) in response to two levels of N fertilization from 2012-2017 in eastern Nebraska, USA. The WSG treatments consisted of (1) switchgrass (SWG), (2) big bluestem (BGB), and (3) low-diversity grass mixture (LDM; big bluestem, indiangrass, and sideoats grama). Soils were sampled by fixed depth increments (0-120 cm) in the WSG plots and in the adjacent corn experiment in 2012 and 2017. Soil stocks (Mg ha-1) of SOC and TN were calculated on an equivalent soil mass (ESM) basis and compared within the three WSG treatments, as well as between experiments (corn compared to the mean of all WSGs). Soil organic C and TN stocks within soil layers and cumulative stocks responded to the main effect of WSG (PWSG<0.05) but were no different when comparing the WSGs to corn (Pexpt=NS). Both SOC/TN stocks and cumulative stocks were generally greater in the LDM compared to BGB. Neither SOC or TN changed over time under either the WSGs or corn. Warm-season grass AGB responded to a three-way interaction of year, N rate, and WSG (P=0.0007). Decreases in AGB over time were significant across WSGs and N levels except for SWG at 56 kg N/ha and LDM at 112 kg N/ ha. Above ground biomass was generally greater in the LDM after the first harvest year (2013). Results suggest that incorporating WSGs into marginal cropland can maintain SOC and TN stocks while providing a significant source of biomass to be used in energy production or in integrated livestock systems.