Carbon sequestration potential of switchgrass as a bio-energy crop
Switchgrass as a bio-energy crop has potential of sequestering carbon in soils.
1. What is carbon sequestration?
Carbon sequestration is a long-term process of storing carbon in oceans, soils, vegetation and geologic formations. Ocean sequestration: carbon can be stored in oceans through direct injection or fertilization, terrestrial sequestration: a large amount of carbon is stored in soils and vegetation, and geologic sequestration: natural pore spaces in geologic formations serve as reservoirs for long-term carbon dioxide storage. In the carbon sequestration process, bio-energy crops can be a sink by sequestering carbon since crops use a lot of carbon dioxide by the process of photosynthesis. Carbon dioxide in the air is taken up by plants and incorporated into living plant matter. As the plants die or are harvested, the carbon based leaves, stems and roots decay in the soil and become valuable organic matter over time.
2. What is the role of soil organic matter in carbon sequestration?
Soil organic matter consists of decomposed plant and animal matter. It helps bind soil mineral particles together into clumps, called soil aggregates. Higher levels of soil organic matter leads to more stable soil aggregates, better soil infiltration capability and aeration, better water holding capacity, more resistance to wind erosion, reduced potential for soil compaction and overall soil fertility. Organic matter also helps hold soil nutrients in place so that they are not lost during erosion, surface runoff or leaching. If left undisturbed, soil organic matter can eventually be transformed into long-lasting humus. However, if the soil is tilled, soil organic matter will be oxidized and the carbon will be lost to the atmosphere as CO2. If the soil erodes, the organic matter will be removed in runoff water.
3. What is carbon sequestration potential of switchgrass as a bio-energy crop?
Switchgrass (Panicum virgatum L.) is a native warm-season perennial to North America and has been used as an erosion control purpose on the road side or sometimes as livestock feed in Midwest or South. Switchgrass has massive root biomass (about 4 dry matter tons per acre) with rhizomes and can go up to 30 feet deep in soil so that it has good potential to sequester carbon in soil as roots decay. According to research conducted in Alabama, the ratio of root to shoot of carbon storage in switchgrass was 2.2 implying that carbon partitioning to roots played an important role in carbon sequestration by switchgrass. In other research done in the central and northern Great Plains, soil organic carbon increased significantly at 0-12 inches and 0-47 inches, with accrual rates of 0.5 and 1.3 ton carbon/acre/yr (equivalent to 1.8 and 4.7 ton CO2/acre/yr), respectively.