Switchgrass is a warm-season perennial grass native to North America and the high cellulosic content of Switchgrass makes it a favorable feedstock for ethanol production. This publication examines planting, seeding rates, harvesting, biomass production and yields.
Growing and Havesting Switchgrass
Using Switchgrass for Forage
Switchgrass is a warm-season perennial grass native to much of the United States. Over the last few years it has received renewed interest as a renewable fuel source, since it produces large amounts of cellulose that can be digested and converted to ethanol. The high yields and environmental adapt-ability of switchgrass make it an excellent choice for biofuel production. While there has been a great deal of media attention on the merits of switchgrass as a biofuel feedstock, many are less familiar with the potential of switchgrass as a forage crop. Switchgrass, like a number of other native warm-season grasses (NWSG), can actually produce high-quality forage. Yields of 2-5 tons per acre can be expected, depending on rainfall, soil type, as well as other environmental conditions. The nutrient content of this forage can be as high as 16-17 percent crude protein, if harvested correctly.
What characteristics make Switchgrass attractive as a forage crop?
Are there keys to using Switchgrass as a hay crop?
Can Switchgrass be grazed?
How to fertilize Switchgrass for forage production?
What about other native grass species?
What characteristics make Switchgrass attractive as a forage crop?
Even though many people are currently focused on switchgrass as a biofuel, it should be kept in mind that switchgrass can also be used as a forage crop. High yields and good quality forage can be produced during summer, if it is managed correctly. If switchgrass is cut while it is young and leafy, the nutrient content will be equal to other grasses. If switchgrass is allowed to mature and become fibrous, forage quality will suffer drastically. Of course, the tendency of switchgrass to produce high amounts of fiber when mature is what makes it desirable for biofuel production.
It should also be kept in mind that this crop does not have to be used only for forage or only for biomass. It can be harvested as a dual purpose crop, so early growth can be used for forage, and later growth can be used for biomass. Haying early may reduce biomass production, but the ability to use some of the growth for cattle production will add flexibility to a producer’s operation, and the opportunity to increase profitability.
► High yields- Switchgrass grown for forage can produce up to twice as much as tall fescue on an acre of land. Research in Tennessee has shown that, if grown exclusively for hay, 4-5 tons per acre are not uncommon. If switchgrass is planted primarily for biofuels production, there is potential to harvest the early growth through haying or grazing, then managing the remainder of the season’s growth for biofuels.
► Summer production- Since switchgrass is a warm-season grass, it is adapted to hot, summer conditions. As peak growth occurs from May through September, it is easy to produce hay because of better drying conditions. It is not unusual to find switchgrass hay that is better quality than the average tall fescue hay This is not because switchgrass as a species is better than tall fescue, but because hay making conditions are better during the switchgrass growing season and because rain and cool temperatures often delay cutting tall fescue. Delayed tall fescue harvest results in decreased protein and energy.
The summer growth of switchgrass also makes switchgrass an excellent forage for grazing. Since most cattle operations in the mid-South use tall fescue as their primary pasture grass, there is limited forage production during summer. This limited production reduces the performance of grazing cattle, and may lead to overgrazing and weakened stands of tall fescue. Switchgrass can provide good quality forage for grazing animals and provide the opportunity to rest tall fescue pastures during a stressful time of the year.
Research has shown switchgrass can be grown successfully as both a biofuel and forage crop. There is no need, however, to grow it as only one or the other. There is the possibility of having switchgrass as a “dual purpose” crop. The early growth of the forage, which is generally the highest quality, can be hayed or grazed. The later growth can be allowed to mature and harvested after frost as a biomass crop. Biomass production will be lower under this scenario, but, depending on the objectives and needs of the producer, may be a useful strategy.
Are there keys to using Switchgrass as a hay crop?
Early-season production (late April – late May for switchgrass) produces the highest quality forage and can be easily diverted for hay. Crude protein levels could easily range from 14 - 20% at this time of the year. However, forage yields will be relatively low (e.g., 2 tons/ac depending on the timing of harvest). As with any hay crop, waiting a few weeks will increase yield and decrease quality (Fig 1.). The later the forage is harvested, the greater reduction in the final biofuel harvest for that season. Most biomass accumulation in switchgrass occurs in the first half of the growing season. In one southeastern study, 56% of annual biomass accumulation was obtained by late June each year. Obviously, delaying the forage harvest too late (past late boot stage) would also be counterproductive for forage production because of drop in forage quality in the maturing stand.
Unlike dormant-season harvests, these early forage harvests (haying or grazing) should leave a minimum 8-inch residual height to ensure rapid regrowth and an adequate final biofuels harvest. Producers must realize that leaving high residual heights is very important to quick recovery of the plant because of the elevated growing point on switchgrass (often > 5” above the soil surface) and the minimal leaf surface area present below 8 – 10”. Removing the growing point and all leaves will result in delayed regrowth that will substantially reduce final yields and, in the long run, stand vigor.
Because biorefineries will require switchgrass on a year-round basis, producers would have the opportunity to sell switchgrass harvested for hay later as biofuels if they find they do not need as much as hay. While dormant-season harvested material is considered better quality for biofuels as a result of reduced mineral concentrations, there is no reason to believe mid-summer “hay” crops will not be acceptable for biofuels. Following guidelines for proper hay storage will help ensure the material will be valuable for hay or biofuels in the future.
"Caution" About Horses and Switchgrass Hay- While switchgrass hay has excellent value for beef and/or dairy cattle, as well as other livestock, there is evidence that horses fed switchgrass hay may have a phototoxic reaction. In short, horses may lose some hair and suffer sunburns. Although it is not common, this problem is something horse owners should be aware of. At this time, switchgrass is not recommended for horse hay.
Because early-season switchgrass has good nutritive value for cattle, the material could be removed through controlled grazing rather than haying. Grazing, of course, requires adequate fencing, access to water and shade. Where this infrastructure is lacking, the investment may not be cost-effective, given the relatively short grazing season that would be available in an integrated system where a good deal of growth will be reserved for biofuels. On the other hand, temporary fencing and leaving gates open back to water on other pastures could be effective; this will be more effective later in the spring when the quality and production difference between cool-season grasses and switchgrass is more pronounced.
Because of the reasons given above under haying guidelines, it is important not to graze switchgrass it too closely. Leaving a residual stand height of at least 8 inches, and preferably as high as 12 inches, will result in more rapid regrowth and greater yields for biofuels at the end of the season. While most producers managing switchgrass strictly as a forage crop will practice rotational grazing to accommodate this growth, it is unnecessary when attempting to integrate grazing and biofuels production. That is because only 2 – 4 weeks of grazing should be planned, which would be a single rotation. Switchgrass could be grazed later into the season, but as with haying, increased consumption as a forage crop will reduce final biomass yields.
Initial entry into switchgrass in the spring should occur once the stand is 18 – 24 inches tall, typically mid-May. Stocking at lower rates or creep grazing calves will make it possible to begin sooner. Stocking rates of 3 – 5 steers/ac will probably be best under normal circumstances. This should allow enough animals to remove the available forage within a 2 – 4 week period, freeing up the remainder of the growing season for accumulation of biofuels. Experience will dictate how to adjust these stocking rates to achieve desired results. Keep in mind, during the establishment year, no grazing should be planned unless it is a brief period of high stocking to remove a weed canopy. During the second year of the stand, there will be production, but it will likely be only 50 – 70 percent of the stand’s potential. It is important to not overgraze the stand this second year to enable the root system to fully develop. Such a system will ensure full production levels in future years and promote considerable stand longevity typical of switchgrass (> 15 years).
How to fertilize Switchgrass for forage production?
Even though these grasses are adapted to poor soil fertility, in order to produce large amounts of high quality forage, adequate levels of potash, phosphate and nitrogen should be provided. Also, best production will occur when soil pH is kept above 6.0. This can be monitored through soil testing once every 2-3 years. Nitrogen should be only be applied to native grasses if soil moisture is not limiting, and if extra forage production is desired (Table 1).
What about other native grass species?
Selection of grasses other than switchgrass can enhance the stand as forage and wildlife habitat. Grasses such as big bluestem, little bluestem and indiangrass have been planted along with switchgrass to form a mix grass stand. Each of these grasses have a slightly different maturity date, which spreads out the potential timing of quality forage harvest. These mixtures also contribute to a different sward structure, which can provide better wildlife habitat than a single grass species. There is also the possibility to use legumes to improve forage quality and to replace nitrogen fertilizer. Research is still needed to identify the proper legume species and management techniques for successful use of legumes in the stands.
A recent study indicated mixed stands produced more net energy than switchgrass monocultures, though the study focused on poor sites unlikely to be used in today’s agriculture. Even though the current focus for biofuels is on switchgrass, there is the possibility that these mixed stands may be acceptable for ethanol production, once the process becomes more developed.
USING SWITCHGRASS FOR FORAGE
Gary Bates, Professor, Plant Sciences
Pat Keyser, Associate Professor, Forestry, Wildlife, Fisheries
Craig Harper, Associate Professor, Forestry, Wildlife, Fisheries
John Waller, Associate Professor, Animal Science
