Management Guide for the Production of Switchgrass for Biomass Fuel Production in Southern IowaAlan Teel |
Paper presented at BioEnergy '98: Expanding Bioenergy Partnerships, Madison, Wisconsin, October 4-8, 1998.
A switchgrass to energy project was commissioned by the Department of Energy in 1992 and was to be carried out by the Chariton Valley Resource and Conservation and Development (CVRC&D) located in Centerville, Iowa. The goal for the project is to use a renewable resource (switchgrass) that can be grown in southern Iowa as a feedstock material to generate electrical energy. The electrical generation plant is a 750 megawatt coal fired facility located in Chillicothe, Iowa. The objective of the project is to co-fire at the rate of 5% switchgrass and 95% coal. This ratio would create the need for 200,000 tons of switchgrass per year.
The feedstock delivery portion of the project will need to deal with issues of production, harvest, storage, transportation and processing. Traditional management practices were evaluated regarding their usefulness in meeting the requirements of this project. Results of this evaluation were that some traditional practices were applicable but others were not and needed some modification.
Our conclusions are that we can produce switchgrass in the quantities needed in a co-fire situation with coal, however some modification of certain production practices will be necessary. Keywords: Feedstock production, feedstock management, switchgrass, coburning.
The use of switchgrass as a dedicated feedstock is a relatively new concept in Southern Iowa. Co-firing with coal to generate electricity or the use of switchgrass for any other purpose other than as a livestock feed was virtually unheard of until 1992, the beginning date for this project. The existing knowledge base was for the production of feed quality forage for use in livestock nutrition. The primary objective of the switchgrass feedstock development portion of the project was to evaluate the known traditional practices for producing switchgrass and to then adapt them or change them to fit the needs of biomass feedstock production.
Ultimately the project will need to produce and deliver 200,000 tons of switchgrass to the 750 Megawatt generating plant at Chillicothe, Iowa to replace 5% of the coal being used annually. This would require the production off 40-50,000 acres of switchgrass given the current expected yields of 4-5 tons per acre. This type of production would have major impacts on soil erosion, water quality and income in the immediate area around the generation plant. What we have learned and are learning about the production of switchgrass as a biomass feedstock will be applied to many other uses of switchgrass as a biomass feedstock that have been discovered and that will be discovered in the future. Some examples of these uses are: fuel pellets for wood pellet stoves, paper, fiberboard, alcohol, animal bedding and mulch.
Switchgrass is a perennial warm-season grass native to all parts of Iowa as well as to other parts of the midwest. It has excellent burn qualities, is easily managed and attains reasonable yields without the use of high rates of nitrogen. Switchgrass adapts well to numerous soil types and climatic conditions allowing it to grow on both the loess and till derived soils in southern Iowa as well as other parts of Iowa.
Since switchgrass seed varies greatly in purity and germination, it is often sold on the basis of its "pure live seed" (PLS) percentage. Seed lots with equal amounts of PLS may differ in their volume of bulk seed. Consider this when calibrating seeding equipment. Newly harvested switchgrass can have a high percent dormancy. Acceptable germination levels are often achieved after one year of storage. For newly harvested seed, a dormancy rating of 10 percent or less is excellent. Planting high dormancy seed in February or early March will help to break the dormancy and improve stand establishment. Cave-in-rock is the variety being recommended at this time. Other varieties are currently being tested and developed and will be recommended if they are shown to have superior burn qualities, are well adapted to Iowa climate and will yield comparatively.
The two most common approaches to establishing switchgrass are to plant into a tilled seedbed or into a herbicide-killed sod using no-till planting equipment. A standard soil test the autumn before seeding should be used as a guide for the need to apply lime, potassium and phosphorous. Soil pH should be 6.5 or higher; potassium and phosphorous levels need only be in the medium range. No nitrogen is recommended for the seeding year.
A firm seed bed is a requirement in order to achieve good seed soil contact. This is not a problem in a no-till situation, however if the soil has been tilled a packing devise must be used to firm the soil. The soil should first be packed so that a footprint is barely visible before seeding. Use of the packing devise again after the seed is planted will usually give better results. Seed should be planted no more than 1/4 to 1/2 inch deep. Deeper seed placement will result in poor emergence and a thin stand.
Weed control is critical to getting a good stand. Weeds need to be controlled from time of seeding through the end of the seeding year. Various herbicides can be used to control weeds during the seeding year. Be sure to read the label carefully for application rates and stages of growth. Some herbicides that are recommended for use on switchgrass have very low rate tolerance, applying too much material or applying it at the wrong time can cause serious injury to the switchgrass seedling. Weeds may also be controlled by mowing at a stubble height of 4-5 inches when weeds are 6 inches or less in height. Care should be taken to not clip the new switchgrass seedlings. Mowing may need to be done several times during the first growing season.
One of the strong reasons for using switchgrass as a biomass feedstock is the low management requirement during the production years. Because it is a perennial there is no need to replant the crop after a successful establishment. Based on the productivity of soils in southern Iowa, 90-120 pounds of nitrogen should be applied annually. After three years of production a soil test should be used to determine the need for additional potassium and phosphorous. We are still uncertain as to the amount of P & K that will be removed under a biomass feedstock system.
Harvesting as a biomass feedstock should be started two to three weeks after a killing frost which is four or more hours at 28 degree F. The moisture content of the switchgrass should be at 15 percent or less so baling can immediately follow a mower/conditioner or windrower. Harvesting at a six inch stubble height will avoid crown and lower stem injury, provide cover for wildlife and collect snow that will provide water for spring green-up. Switchgrass can be baled in large round bales, large square bales, small square bales, or it may be chopped. Harvesting method will be dependent on or any combination of available equipment, end use of the feedstock, storage time, required distance to be transported, and costs.
Old established stands of switchgrass that have not been well managed may need to be renovated. Identifying the reason for a low-yielding switchgrass stand is the first step in the renovation process. Several possibilities may include: low fertility levels, weed competition, inadequate stand density (less than one plant per square foot) or any combination of these factors.
Soil testing will aid in determining the levels of P & K present and the soil pH. Applying the recommended rates should correct any nutrient deficiencies. Weed competition can be more difficult to address. Weeds may become a problem in the seeding year or gradually invade stands as they thin. Thinning can result from improper harvest management, low fertility or conditions causing bare soil such as harvest damage, rodent burrowing, and erosion. Correcting the cause of the thinning stand can advance successful weed control. Burning has been used successfully in some situations for weed management in switchgrass, especially for controlling perennial weeds and brush. In some cases, burning can increase the vigor and productivity of the stand. Burn in late winter or early spring before new swithcgrass plants are actively growing.
Currently we are managing switchgrass for biomass feedstock as a one cut crop. In the future we need to begin to look at this crop as part of a production system that may have production potential above the one cut level. This may provide us the opportunity to have more front-end, high value production that could add to overall profitability by increasing our production and reducing our input cost. For example, we may be able to grow a legume crop interseeded into the switchgrass that could be harvested early, before the switchgrass starts to grow, and then allow it to provide the nitrogen needed for the switchgrass thus reducing our production costs. Growing the switchgrass in rows and cropping the inter-row area has not been explored and may, in some climates, increase our productivity and profitability.