Soil Carbon Storage by Switchgrass Grown for Bioenergy

Abstract

Life-cycle assessments (LCAs) of switchgrass (Panicum virgatum L.) grown for bioenergy production require data on soil organic carbon (SOC) change and harvested C yields to accurately estimate net greenhouse gas (GHG) emissions. To date, nearly all information on SOC change under switchgrass has been based on modeled assumptions or small plot research, both of which do not take into account spatial variability within or across sites for an agro-ecoregion. To address this need, we measured change in SOC and harvested C yield for switchgrass fields on ten farms in the central and northern Great Plains, USA (930 km latitudinal range). Change in SOC was determined by collecting multiple soil samples in transects across the fields prior to planting switchgrass and again 5 years later after switchgrass had been grown and managed as a bioenergy crop. Harvested aboveground C averaged 2.5± 0.7 Mg C ha −1 over the 5 year study. Across sites, SOC increased significantly at 0-30 cm (P=0.03) and 0-120 cm (P=0.07), with accrual rates of 1.1 and 2.9 Mg C ha −1 year −1 (4.0 and 10.6 Mg CO 2 ha −1 year −1 ), respectively. Change in SOC across sites varied considerably, however, ranging from −0.6 to 4.3 Mg C ha −1 year −1 for the 0-30 cm depth. Such variation in SOC change must be taken into consideration in LCAs. Net GHG emissions from bioenergy crops vary in space and time. Such variation, coupled with an increased reliance on agriculture for energy production, underscores the need for long-term environmental monitoring sites in major agro-ecoregions.

Dedicated Energy Crops and Crop Residues for Bioenergy Feedstocks in the Central and Eastern USA

“…In the Central USA, SOC sequestration in switchgrass production systems occurred in a 5-year on-farm study of 10 sites across Nebraska, South Dakota, and North Dakota [45,89]. In eastern Nebraska, both switchgrass and corn biomass production systems sequestered SOC after nine continuous years in both annual and perennial biofuel systems.…”

“…Use of perennial grasses on landscapes, especially where soils are marginally productive and/or erosion prone, has been shown to enhance SOC storage and nutrient retention (i.e., P), improve soil bulk density, and reduce erosion risk [45,89,99]. Although direct plant measurements of switchgrass grown under higher atmospheric CO 2 concentrations indicate that switchgrass may be limited in its potential to boost productivity as atmospheric CO 2 concentrations increase [100], model simulations of drought-tolerant cultivars predict switchgrass could withdraw between 3 and 19 % less water than conventional crops under future climate change scenarios [101].…”

Soil Carbon Sequestration by Switchgrass and No-Till Maize Grown for Bioenergy

“…Most of the research on SOC in agricultural production systems focused on C in the 0 to 30 cm depth [22][23][24][25][26][27]. A few studies in which soil sampling has been conducted at greater depths indicate that production agriculture affects soil C deeper in the soil profile [28,29].…”

From Tiny Microalgae to Huge Biorefi neries

“…corn stover, dedicated perennial energy grasses) are expected to have lower GHG emissions than conventional gasoline or corn grain ethanol [9][10][11][12][13]. Furthermore, dedicated perennial bioenergy crop systems such as switchgrass (Panicum virgatum L.) have the ability to significantly increase SOC [14][15][16] while providing substantial biomass quantities for conversion into biofuels under proper management [17,18].…”