Strategic switchgrass (Panicum virgatum) production within row cropping systems: Regional soil erosion loss and water runoff impacts

Authors: WANG, E - Iowa State University; CRUSE, R - Iowa State University; SHARMA-ACHARYA, B - Oklahoma State University; HERZMANN, D - Iowa State University; GELDER, B - Iowa State University; James, David; Flanagan, Dennis; BLANCO-CANQUI, H - University Of Nebraska; Mitchell, Robert - Rob; LAIRD, D - Iowa State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2020
Publication Date: 9/4/2020
Citation: Wang, E., Cruse, R.M., Sharma-Acharya, B., Herzmann, D.E., Gelder, B.K., James, D.E., Flanagan, D.C., Blanco-Canqui, H., Mitchell, R., Laird, D.A. 2020. Strategic switchgrass (Panicum virgatum) production within row cropping systems: Regional soil erosion loss and water runoff impacts. Global Change Biology Bioenergy. 12:955–967. https://doi.org/10.1111/gcbb.12749.
DOI: https://doi.org/10.1111/gcbb.12749

Interpretive Summary: Soil erosion accelerated by human activities is a destructive process that can diminish the productivity of agricultural lands and negatively impact off-site water quality. Practices that can reduce water runoff and soil loss include growing perennial crops (e.g. switchgrass) that provide long-term surface cover and subsurface root biomass and much lower soil disturbance, all of which decrease the potential for erosion by water. Perennial switchgrass can also be harvested as a bioenergy crop. In this research, we used a web-based erosion computer simulation modeling tool, the Daily Erosion Project, to estimate what the effect would be of converting existing cropping systems (typically corn-soybean rotations with substantial tillage operations) to growth of continuous switchgrass for three scenarios: on hillslopes with average slope steepness > 3%, > 6%, and > 10%. The simulations were conducted over eight major land resource areas covering all or parts of Iowa, Missouri, Minnesota, Wisconsin, and Illinois using observed weather data from 2008-2016. Results showed that replacing row crops with switchgrass reduced average annual soil loss by 43.7-95.5% compared with the baseline levels. The greatest soil loss reductions were seen when switchgrass was grown on all hillslopes with average slope steepness > 3%. These results impact soil conservation agency personnel, policy makers, scientists, university faculty, extension agents, farmers and others with interests in reducing erosion and conserving soil resources. Use of alternative bioenergy crops such as switchgrass may provide for substantial soil conservation on marginal steep lands prone to erosion by water.

Technical Abstract: A strong need exists for tools to assess the efficacy of conservation practices across large regions that support informed policy decisions that may lead to better soil and water conservation while optimizing agricultural production options. Perennial warm-season grasses (WSGs) such as switchgrass (Panicum virgatum), for example, can be grown on marginally productive and/or environmentally sensitive lands to meet growing bioenergy demands while reducing water runoff and soil erosion compared to current row crop systems. Quantifying the effect of WSG production where most appropriate on the landscape would help support decisions favoring both economic and environmental benefits. We used the Daily Erosion Project (DEP) to simulate the effects of WSGs on hillslope water runoff and soil loss for 2008-2016 across eight major land resource areas (MLRA) in the Midwest US. Four different scenarios (baseline or existing conditions and switchgrass grown on slopes = 3%, = 6%, and = 10%) were modeled. Across all hillslope groups replacing row crops with switchgrass reduced yearly water runoff and soil loss by 3.2-12.1% and 43.7-95.5% compared with the baseline levels, respectively. Water and soil conservation efficiency (water runoff reductions or soil loss reductions associated with one percent increase in switchgrass coverage), increased with slope, 10% > 6% > 3% for all MLRAs. With baseline conditions, the soil loss estimates for the four most vulnerable MLRAs were above what is considered tolerable in the US (11.2 Mg/ha/yr); switchgrass replacement on slopes = 10% reduced average soil loss estimates as much as 22.6 Mg/ha/yr for the most erosive MLRA and resulted in all MLRA erosion estimates = 6.0 Mg/ha/yr. For soil loss, an apparent interaction existed between slope group and total annual precipitation; as annual precipitation increased the difference in soil loss between slope groups increased. Soil loss was more sensitive to these factors than was water runoff. Strategic placement of WSGs on sloping lands has the potential to reduce land degradation and adverse environmental impact of row crop production while supporting a growing bioenergy industry.