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The Center for Native Grasslands Management

Projects: Forages

Switchgrass Cutting Height Study

There is increasing interest in managing switchgrass in the Mid-South for both biofuel and forage production. Evidence suggests that low cutting heights will weaken switchgrass stands, thus reducing future yields and increasing weed invasion. However, there is no published data comparing multiple cutting heights on switchgrass or documenting optimum cutting heights for maintaining stand vitality and yield over time.

Using existing mature switchgrass stands, an experiment was conducted to document response over a cutting height gradient for three widely used varieties of switchgrass. A completely randomized block design with two factors was used. Factors were cutting height (4, 8, 12, and 16 inch stubble height) and variety (Cave-in-rock, Alamo, and Kanlow) all replicated four times. Two harvests were taken in 2007 through 2011, with timing of harvest set to that of a hay production system. Results indicate that Kanlow, Cave-in-rock, and Alamo switchgrass will produce comparable yields given similar growing conditions. Additionally, harvesting switchgrass at shorter heights did not necessarily produce higher yields. Yield differences in cutting height became more apparent after year two of the experiment, which suggests that a shorter cutting height (4-in) has negative impacts on sustaining long-term yields and stand viability in a two-cut system.   

Cutting height study, 2011. Experiment is being conducted on the Plant Science Unit's 20 year-old switchgrass stand.

NOTE: Also see biofuels page for the integrated forage/biofuels project.

Grazing Winter Annuals in Native Grass Forage Systems

Native warm-season grasses (NWSG) forage producers may want to take advantage of native grasses’ relatively long dormant season by “double-cropping” with winter annuals. This approach has long been used with bermudagrass. If a system can be developed that maintains the viability of the NWSG stand, this approach could make NWSG a more attractive alternative for producers.
We will establish winter wheat and annual ryegrass into existing stands of switchgrass and a big bluestem/indiangrass mix. Stands will be grazed by steers during the winter months in a randomized block design using 3-ac paddocks. Work will be conducted at Middle Tennessee Research and Education Center. Gains and NWSG stand quality will be monitored and compared to stockpiled fescue-red clover. NWSG stand condition with winter annuals will be compared to an un-planted and un-grazed control.

Jersey heifer foraging on switchgrass at Middle Tennessee Research and Education Center.

Switchgrass Establishment Studies

Switchgrass is anticipated to become a major crop in Tennessee both for the emerging biofuel industry, as well as for integrated forage systems. This species has many ecological benefits as it sequesters significant amounts of carbon, provides wildlife habitat, and requires low amounts of synthetic-nitrogen. However, one major obstacle for large-scale switchgrass production is consistent stand establishment. Assumed, but largely untested establishment strategies include dormant-season planting and utilizing winter annual nurse crops in order to reduce weed incidence; however, the success of these approaches have not been well-documented.

The first study evaluated the efficacy of no-till planting into winter annuals for improved stand establishment by i) evaluating switchgrass yield, density, and height when planted into winter annuals (wheat, rye, barley, and oats), and a fallow control; and by, ii) evaluating three seeding dates (March, May, and June) into each of these winter annuals and the control. Plots were established in 2009 and 2010 in a split-block design, with three replications at three sites in Tennessee. Switchgrass frequency for the establishment year 2009 differed by location, and overall success was low and patterns among locations were not consistent. Switchgrass yield was generally greatest when planted in either March or May.  For both years, oats, barley and wheat were among the best winter annual treatments; and, all visually aided in establishment compared to the fallow control. Establishment in 2010 was generally greatest when planted in March or May for all locations. Overall, this study indicates that integrating winter cover crops promotes switchgrass stand establishment and may prove to be a promising management practice in the Southeast for the emerging biofuel industry.

Initiation of the study utilizing small grains to aid in switchgrass establishment, Plant Sciences Unit, Knoxville, TN.

The experimental objective of the second study was to test the efficacy of dormant-season planting to enhance switchgrass establishment in the upper-South. Specifically by: i) evaluating three dormant-season planting dates versus a growing-season control; ii) evaluating two seeding rates for dormant-season planting; and, iii) by comparing high and low dormancy seed lots for both rate and date combinations. Four planting dates (1 December, 1 February, 15 March, and 1 May), two seeding rates (6 and 9 lbs PLS ac-1), and two dormancy groups (high and low) were established at two locations in Tennessee. Switchgrass frequency differed, but overall success was low and patterns between the two locations were not consistent. For both years, seed dormancy levels and seeding rates did not affect establishment success. Generally, switchgrass frequencies were visually greatest when planted in March, and yield was visually highest when the high-dormancy seed lot was used. Therefore, seeding at a higher rate may cause negligible effects and may not prove to be economically practical; however, these results need to be validated over a wider range of soils and climatic conditions. Nevertheless, planting under dormant-season and high-dormant seed conditions may be utilized as a management tool to aid in switchgrass stand establishment and increase the cellulosic production for producers in the Southeastern U.S.

A Forestry, Wildlife & Fisheries student conducting vegetation sampling to quantify wildlife habitat on native warm season grasses at one of the Conservation Innovation Grant study sites.

Lastly, a third experiment is underway to validate successful treatment results from the two establishment studies mentioned above (dormant-season and small grain study). This experiment will evaluate the efficacy of dormant season plantings and insecticide treated seed of NWSG in winter wheat cover crop systems in the upper South.  Specifically, by: i) evaluating the winter wheat cover crop stand effect on NWSG establishment, based on ‘good’ and less vigorous or ‘poor’ stands of wheat; ii) testing NWSG establishment and efficiency of insecticide/fungicide (Gaucho XT) treated seeds;  and, iii) comparing wheat stand establishment, insecticide and non-insecticide treated amongst switchgrass, big bluestem, and gamagrass populations when dormant-season planted. The whole plot design is winter wheat fertility rates (good and poor: 60 versus 0 units ac-1, respectively).  The split-plot treatments include insecticide treated and non-treated seed of native warm season grasses. The experimental treatment combination will be replicated 3 times and over 2 locations.