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What is switchgrass

Switchgrass (Panicum virgatum) is a summer perennial grass that is native to North america. It is a natural component of the tall-grass prairie which covered must of the great Plains.

Because it is native, switchgrass is resistant to many pests and plant diseases, and it is capable of producing high yields with very low applications of fertilizer. This means that the need for agricultural chemicals to grow switchgrass is relatively low. Switchgrass is also very tolerant of poor soils, flooding and drought, which are widespread agricultural problems in the southeast.

There are two main types of switchgrass: upland types, which usually grow 5 to 6 feet tall and are adapted to well drained soils, and low land types, that grow up to 12 feet tall and which are typically found on heavy soils in bottomland sites. Although switchgrass is native, plant breeders have developed a fairly large number of improved varieties for use as forage.

‘Alamo’ switchgrass is a robust lowland variety of switchgrass most suited to the southern US. In Auburn University test plots, it has frequently produced over 10 tons per acre per year, but on a commercial scale, it is more reasonable to expect 6 to 8 tons per acre. This is because test plots usually have perfect establishment, but commercial plantings almost always have weak spots in the field. However, for comparison, the average annual hay yield for Alabama is about 2.5 tons per acre, and the productivity of forests is only about half that of switchgrass.

The seed of switchgrass is very small, and much of it is dormant (will not germinate) right after it is harvested. However, aging, treating it with water and chilling temperatures (stratification) or storing it in warm conditions will break dormancy.

Partly because of the small size of the seed, switchgrass seedlings tend to be slow to develop, and are susceptible to weed competition. Unfortunately, there are no herbicides approved by government for weed control during establishment of switchgrass. However, it can still be successfully established by no-till planting and other strategic approaches.

Switchgrass reaches full yield only in the third year after planting; it produces a quarter to a third of full yield in the first year, and about two thirds of full yield in the second year. When managed for energy production it can be cut once or twice a year with regular hay or silage equipment.

At maturity, widely spaced switchgrass plants can measure 20 inches in diameter at ground level. Switchgrass has a huge, permanent root system that penetrates over 10 feet into the soil, and weighs as much (6-8 tons/acres) as the above-ground growth from one year. It also has many fine, temporary roots. All these roots improve the soil by adding organic matter, and by increasing soil water infiltration and nutrient-holding capacity. Switchgrass fields provide habitat and a home for many species of wildlife, including cover for deer and rabbits, and a nesting place for wild turkey and especially quail.

Switchgrass has several other environmental benefits. If it is used to produce energy, it will reduce the risk of global warming by replacing fossil fuels (coal, natural gas and oil). When fossil fuels are burnt, carbon is removed from below ground (gas and oil wells and coal mines) and release into the atmosphere as carbon dioxide (CO2). This is a greenhouse gas that increases the risk of global warming. In contrast, switchgrass (like all other plants) removes CO2 from the atmosphere and incorporates it into plant tissue, both above and below the ground.

Carbon cycle Switchgrass cycles and sequesters atmospheric CO2, thus reducing the risk of global warming.
The accumulation of carbon, especially below the ground, is known as carbon sequestration, and is considered to be a very important strategy for reducing atmospheric CO2. Switchgrass is unquestionably one of the best crops for doing this. when above-ground switchgrass is harvested and burned for energy, CO2 is once again returned to the atmosphere from where it was originally obtained by the plant, but it will have reduced the need for some fossil fuel. Therefore, CO2 is obviously just being recycled by use of switchgrass for energy, making this process CO2-neutral (or actually CO2– negative if soil carbon sequestration is considered), compare to fossil fuels that add CO2 to the atmosphere. when compared to low grade coal, burning switchgrass for energy will probably result also in less toxic emissions, such as the oxides of sulphur and nitrogen.
Atmospheric carbon Fossil fuels add CO2 to the atmosphere thus raising the risk of global warming.
Together with its energy benefits, swicthgrass offers great opportunity for farmers. Because of its perenniality, compared to annual crops switchgrass is a true conservation crop which will substantially reduce soil erosion and release of soil carbon which are related to annual tillage, and it will reduce the use of toxic chemicals. It could also produce much needed farm income in many regions that are in desperate need of rural development, and it could substantially reduce the need for farm programs and disaster aid which are currently paid from tax dollars.
What is needed to ensure that we fully realize all these potential benefits? Simple! We must demonstrate that the process of using switchgrass for energy can be profitable — for energy producers, farmers, and consumers of energy.

Can this be done? Probably – especially in certain specific situations, and co-firing switchgrass with coal to produce electricity in existing plants offers on of the best near-term prospects. Perhaps most important, we must recognize that fossil fuels will be our main energy base for many years, and bioenergy from switchgrass is not intended to compete with these valuable resources, but rather, to complement them by softening their environmental impact.

David Bransby, University of Auburn

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Written by Casey McConnell

February 13, 2008 at 3:17 pm

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