Environmental Impacts
Environmental Impacts
Soil Erosion Control
Planting switchgrass on croplands dramatically reduces soil erosion potential compared to annual row crops. The perennial nature of the crop provides for year-round protection of the soil surface from erosive forces of wind and rainfall after it is established. This is especially true for marginal land, which can be highly erosive.
During establishment, care should be taken to minimize soil erosion. Switchgrass seedlings require one to two weeks to emerge, even under ideal conditions. This presents a real possibility of excessive soil erosion if sufficient residue is not maintained during establishment. Therefore, it is recommended some crop residue remain on top of the seedbed for erosion control. Furthermore, success with direct seeding of switchgrass into previous crop stubble has been reported, which would provide for optimum erosion control during establishment. Utilization of a non-competitive companion crop with switchgrass also provides for erosion control and may provide a level of weed suppression.
Carbon Sequestration and Greenhouse Gas Offsets
The soil carbon content of cropland soils has been reduced through long-term cultivation. Cultivation enhances soil aeration and accelerates the break down of soil organic matter, the main source of soil carbon. Growing switchgrass provides an opportunity to sequester carbon in soil because tillage is removed from the system. Also, perennial grasses such as switchgrass can deposit organic matter deep within the soil profile as roots expand into the subsoil for nutrients and water.
Sequestration of carbon in soils removes CO2 from the atmosphere, which is considered a greenhouse gas contributing to global climate change. Its reduction in the atmosphere is one benefit of utilizing switchgrass as a fuel source to offset CO2 emissions from the combustion of fossil fuels. Much of the offset results from the fact that ethanol use reduces gasoline combustion. However, some CO2 offset results from sequestration of carbon in soils, particularly in soils cultivated prior to switchgrass establishment. Establishment of switchgrass on Conservation Reserve Program (CRP) land or rangeland, results in little or no net increased soil carbon sequestration because these systems contain relatively high levels of soil carbon; therefore, carbon accumulation is limited compared to previously cultivated land.
CRP Opportunities and Concerns
There is much debate about the role of CRP lands within the developing biofuels industry. Many wildlife conservation groups are concerned that a biofuels industry centered on grain-based ethanol will cause CRP lands to be converted to annual grain crops, which will reduce wildlife habitat quality. A cellulosic biofuel industry fed by perennial grasses such as switchgrass could provide for a good compromise because switchgrass, even when grown in a monoculture, is reported to provide higher quality habitat than annual cropping systems. In addition, switchgrass production provides for soil conservation and minimizes nutrient runoff to surface water bodies; thereby, providing the benefi ts originally intended for the CRP program.
Biodiversity and Wildlife Habitat
Switchgrass can provide habitat and food for many species of wildlife, including cover for large and small mammals, and a nesting place for wild turkey and quail. Even as a monoculture, it is better suited than annual grain crops to provide cover, forage, and nesting areas for native species. The fi nal impact of switchgrass planted for biofuel production on biodiversity depends on how it is managed. Converting CRP lands that currently have mixed native grass stands to monocultures of switchgrass may reduce wildlife habitat.
