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Title: Carbon sequestration under irrigated switchgrass (Panicum Virgatum) production

Author
item Collins, Harold
item FRANSEN, STEVE - WASHINGTON ST UNIV
item Smith, Jeffrey

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2010
Publication Date: 9/30/2010
Citation: Collins, H.P., Fransen, S., Smith, J.L. 2010. Carbon sequestration under irrigated switchgrass (panicum virgatum) production. Soil Science Society of America Journal. 74:2049-2058.

Interpretive Summary: Innovative strategies to mitigate threats of global climate change warrant evaluation of crops capable of producing high biomass for both energy generation and promotion of soil organic matter through C sequestration. Bioenergy crops have the potential to reduce the rate of atmospheric CO2 enrichment as well as supply a portion of U.S. energy needs. Perennial herbaceous plants (e.g. switchgrass) have been shown to improve soil quality, enhance nutrient cycling, improve wildlife habitat and sequester C. However, none of this work has been conducted in the PNW. With the increased likelihood of a bio-based energy industry being created in the Columbia Basin of Eastern WA (proposed 115-M L biodiesel and 1100–M L of ethanol facilities), we initiated research (2003) on the production of oilseeds and biomass crops and are just now evaluating secondary benefits of environmental improvement through C sequestration and removal of soil nutrients. Above ground biomass annual yields averaged 20.4 16.9 and 14.5 Mg dry matter ha-1 for the Kanlow, Shawnee, and Cave in Rock varieties, respectively. The cumulative export of C and N from the field at harvest averaged 15.2 Mg C ha-1 and 427 kg N ha-1 among varieties over two years of production. Root biomass produced after three seasons averaged 9.2 Mg ha-1 to a depth of 1-m, with an estimated C pool of 4.1 Mg C ha-1 m-1. On average 24% (~1.8 Mg C ha-1) of the soil C has been derived from the inclusion of switchgrass.

Technical Abstract: Perennial herbaceous bioenergy crops have the potential to improve soil quality, sequester soil C, enhance nutrient cycling, improve wildlife habitat and supply a portion of U.S. energy needs when used as a fuel. Enhanced carbon sequestration combined with bioenergy based cropping systems could potentially offset 1000-2000 Mt C y-1 globally. Assessments of how much C can be sequestered into soil are needed since the C contained in the above ground biomass will be removed from the site of production and used as an energy feedstock. The objective of this study was to characterize soil C inventories under perennial switchgrass (Panicum virgatum) biomass bioenergy crops. Specific objectives were to: 1) determine the contribution of C4 switchgrass belowground production to soil organic carbon, 2) determine mean residence time (MRT) of the native soil C after planting to switchgrass. Only the contribution of C4 grasses is presented here. Switchgrass cultivars Kanlow, Shawnee, and Cave in Rock, produced an aboveground biomass averaging 21.7 18.2 and 15.6 Mg dry matter ha-1 after 3 y, respectively. Cumulative C and N removed in the above-ground biomass after three years averaged 16 400 and 450 kg ha-1 among cultivars, respectively. Root biomass produced after three seasons averaged 9.2 Mg ha-1 to a depth of 1-m after three years. Root C was greater for the upland cultivars, Shawnee and Cave in Rock than Kanlow, with an average of 3.9 Mg C ha-1 m-1 among cultivars. On average 23% (2.4 Mg C ha-1) of the soil C in the 0-30 cm depth increment has been derived from the inclusion of the C4 grass crops. Total C increased an average of 2.2 Mg C ha-1, above the native soil condition, with cropping of upland cultivars (Shawnee and Cave in Rock) showing the greatest increase. Estimated root turnover ranged from 52-57 % of root biomass among cultivars.