Field-scale soil property changes under switchgrass managed for bioenergy

Authors: Schmer, Marty; Liebig, Mark; Vogel, Kenneth; Mitchell, Robert - Rob

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2011
Publication Date: 11/1/2011
Citation: Schmer, M.R., Liebig, M.A., Vogel, K.P., Mitchell, R. 2011. Field-scale soil property changes under switchgrass managed for bioenergy. Global Change Biology Bioenergy. 3: 439-448.

Interpretive Summary: Switchgrass is a perennial grass native to North America. Switchgrass is considered a model bioenergy crop that can be converted to a transportation fuel or used for electricity generation. Managing switchgrass for bioenergy is different than managing it as a hay crop or as forage. Little is known how switchgrass managed for bioenergy will impact soil properties at the field-scale especially if switchgrass is used in a crop rotation. A switchgrass study was initiated on multiple farms in North Dakota, South Dakota, and Nebraska to look at soil property changes over a 5 yr period. We saw changes in soil bulk density, soil pH, soil organic carbon, and soil phosphorous levels. Most soil property changes were small over the 5 yr study with the exception of soil organic carbon. Soil organic carbon levels averaged across locations showed large increases which would indicate that switchgrass can sequester carbon at different soil depths. In general, increasing soil carbon levels has a positive impact in growing food crops. More research is warranted to look at field scale soil property changes in switchgrass for different regions and at different landscapes.

Technical Abstract: The capacity of perennial grasses to affect change in soil properties is well documented but soil property information on switchgrass (Panicum virgatum L.) managed for bioenergy is limited. Potential improvements in near-surface soil function are important should switchgrass be included as a perennial phase within existing cropping systems. An on-farm study (10 fields) located in North Dakota, South Dakota, and Nebraska was sampled using transects across fields prior to switchgrass establishment and after five years to determine changes in soil bulk density, pH, soil P, and equivalent mass soil organic carbon (SOC). Changes in soil bulk density were largely constrained to near-surface depths (0 to 0.05 m) where plant biomass inputs and management influences are greatest. Soil bulk density increased (0 to 0.05 m) at the Nebraska locations (Mean = 0.16 Mg m-3), while most South Dakota and North Dakota locations showed declines in soil bulk density (Mean = -0.18 Mg m-3; Range = -0.42 to 0.07 Mg m-3). Soil pH change was significant at five of the 10 locations at near surface depths (0 to 0.05 m), but absolute changes were modest (Range = -0.67 to 0.44). Available phosphorous (P) declined at all sites where it was measured (North Dakota and South Dakota locations), with decreases most prevalent at the 0 to 0.05 m depth. When summed across the surface 0.3 m depth, annual decreases in available P averaged 1.5 kg P ha-1 yr-1 (Range = 0.5 to 2.8 kg P ha-1 yr-1). Averaged across locations, equivalent mass SOC increased by 0.5 Mg C ha-1 yr-1 and 2.4 Mg C ha-1 yr-1 for the 2500 Mg ha-1 and 10000 Mg ha-1 soil masses, respectively. Results from this study underscore the contribution of switchgrass to affect changes in soil properties over time, though considerable variation in soil properties exists within and across locations. Further long-term evaluations of soil property changes under perennial bioenergy systems are needed at multiple ecoregions and spatial scales.