Published online April 19, 2018

Switchgrass Growth Forage & Grazinglands and Forage Quality Trends Provide Insight for Management

Kenton L. Sena,* Ben Goff, Core Ideas David Davis, and S. Ray Smith • Switchgrass forage quality declines predictably throughout season. Abstract • Switchgrass biomass accumulates predictably during Switchgrass () has been identified as a valuable the season. crop for biomass and liquid biofuels, as a viable summer forage • Seasonal biomass and forage quality patterns may for cattle, and as a dual-use crop for both applications. The objec- permit flexible management. tive of this research was to evaluate trends throughout the growing season in biomass and forage quality of two switchgrass cultivars in central Kentucky over a 2-yr period. Consistent with observed trends about these cultivars, Cave-in-Rock yielded moderate total biomass and had relatively good forage quality through early- mid season growth. Alamo accumulated high total biomass, but demonstrated marginal forage suitability. This research produced trends predicting biomass and forage quality by accumulated growing degree days, and these trends will aid producers in man- aging switchgrass for biomass and/or forage utilization.

Switchgrass for Forage and Bioenergy witchgrass (Panicum virgatum L.), a warm-season grass native across much of eastern North America (Hitchcock, 1935), S K.L. Sena, Dep. of Forestry, Univ. of Kentucky, was once an important component of the tallgrass prairie biome Lexington, KY, 40546; B. Goff, S.R. Smith, Dep. throughout its range, but was largely eliminated by cultivation of and Soil Sciences, Univ. of Kentucky, and the introduction of grazing-tolerant European grasses such Lexington, KY, 40546; D. Davis, Univ. of as tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. Kentucky Extension, Clark County Extension cons.], orchardgrass ( L.) and Kentucky bluegrass Office, Winchester, KY, 40391. *Corresponding ( pratensis L.) (Wolf and Fiske, 2009). Because of its deep-rooted author ([email protected]). structure, switchgrass is well-suited for soil conservation purposes (Lee et al., 2007; Sanderson, 2008; Garten et al., 2010) and has been Received 1 Aug. 2017. Accepted 26 Jan. 2018. widely used in Conservation Reserve Program plantings in the Midwest (Lee et al., 2007). Switchgrass grows well across a range Abbreviations: ADF, acid detergent fiber; AGGD, accumulated growing degree days; CP, crude protein; of environmental and soil conditions, including low-moisture and DDM, digestible dry matter; DMI, dry matter intake; low-fertility soils unsuitable for other crops (Ghimire and Craven, LAI, area index; NDF, neutral detergent fiber; NIRS, 2011; Yost et al., 2017). Switchgrass growth on marginal and low- near-infrared reflectance spectroscopy; RFQ, relative quality soils is well documented, and recent studies have observed forage quality; TDN, total digestible nutrients. good switchgrass production on low-quality reclaimed surface Conversions: For unit conversions relevant to this mine soils in eastern Kentucky (Marra et al., 2013). article, see Table A.

Switchgrass populations across North America have been broadly Crop Forage Turfgrass Manage. classified into ecotypes (i.e., upland or lowland) based on growth 4:170053. doi:10.2134/cftm2017.08.0053 characteristics. Upland cultivars, such as ‘Cave-in-Rock’ and © 2018 American Society of Agronomy ‘Trailblazer,’ are typically fine-stemmed and drought- and cold-tol- and Crop Science Society of America erant, with moderate biomass potential and forage quality. Lowland 5585 Guilford Rd., Madison, WI 53711 cultivars, such as ‘Alamo’ and ‘Kanlow,’ tend to be coarser-stemmed, All rights reserved.

crop, forage & turfgrass management 1 of 8 Table A. Useful conversions.

To convert Column 1 to Column 2, Column 1 Column 2 multiply by Suggested Unit SI Unit Length 2.54 inch centimeter, cm (10–2 m) Area 9.29 ´ 10 –2 square foot, sq ft square meter, sq m Yield and Rate 2.24 ton (2000 lb) per acre, ton/acre megagram per hectare, Mg/ha Temperature 5/9 (°F – 32) Fahrenheit, °F Celsius, °C

with lower drought- and cold-tolerance and greater biomass Table 1. Soil test results from the UK Edenshale and production (Casler and Boe, 2003; Stroup et al., 2003; Fike Spindletop research farms (high P levels at Spindletop et al., 2006b). In addition, upland types reach reproductive are a result of high P in the limestone substrata). maturity earlier than lowland types, exhibiting a latitudinal pH P K Ca Mg Zn Total C gradient in time to maturity (Casler and Boe, 2003). ————————— t / a c —————— ——— % Lexington 6.05 480.0 212.2 5096 315.2 4.0 2.75 Because of its high yields across a range of climatic and soil condi- Eden Shale 5.35 33.2 232.8 4418 324.5 2.9 2.34 tions, switchgrass has been identified as a potentially important crop for bioenergy applications (Mitchell et al., 2008; Lemus et al., 2014; Ashworth et al., 2017). Considerable research has pro- vided insight into optimal management and harvest regimes improved varieties may alter yields and profitability over time for combusting switchgrass to generate electricity (Vogel et al., (Vogel et al., 2013; Delaquis et al., 2014). 2002; McLaughlin and Kszos, 2005; Jung and Lal, 2011; Smith et al., 2013; Hong et al., 2014, Ibrahim et al., 2017). In addition to The objective of this research was to characterize seasonal co-firing with coal, switchgrass has been investigated as a feed- trends in forage quality and biomass yield of switchgrass in stock for cellulosic liquid fuel conversion (Schmer et al., 2008; central Kentucky over a 2-yr period. These trends will enable Vogel et al., 2011; Schmer et al., 2012; Griffith et al., 2014). producers to better predict optimal harvesting times for switchgrass managed for biomass and/or forage purposes. Switchgrass has also been considered for use as a summer forage for cattle (Wolf and Fiske, 2009; Sanderson and Burns, 2010; Davis, 2014). Because it is a warm-season grass, most of Switchgrass Stand Selection its growth occurs during warm months—the period during and Management which cool-season grasses predominately used for grazing Two established switchgrass stands were selected for har- and hay production are typically dormant or at low produc- vesting in this study: a stand of Alamo at the University of tivity (Davis, 2014). Thus, switchgrass could be an important Kentucky Spindletop Research Farm in Lexington, KY (estab- component of grazing and hay production systems for cattle. lished 2007), and a stand of Cave-in-Rock at the University of Kentucky Edenshale Research Farm in Owen County, KY In addition to managing switchgrass for any one of these uses, (established 2001). Cave-in-Rock was planted on an Eden some research suggests that switchgrass can be managed for silty clay loam and flaggy silty clay soil (Typic Hapludalf), multiple applications (Richner et al., 2014). Specific recommen- and Alamo was planted on a silt loam from the Huntington dations for managing multipurpose switchgrass systems are (Fluventic Hapludoll), Lowell (Typic Hapludalf), and Maury complex, and must be tied to individual sites, cultivars, and soil series (Typic Paleudalf) (USDA NRCS, 2017). Soil test markets. Harvest timing and frequency are clearly important results data are shown in Table 1. Nutrient concentrations met factors affecting both short- and long-term biomass and for- University of Kentucky recommendations for switchgrass. age yields (Lee et al., 2007; Trócsányi et al., 2009; Guretzky et Nitrogen (60 lbs N/ac) was applied to both stands in both years al., 2011; Kering et al., 2013; McIntosh et al., 2016), but stand in early May (Smith et al., 2010, UK CAFÉ, 2015). Both stands management endpoints for forage and biomass are conflict- were treated with 2,4-D at a rate of 2 qt/ac both years in early ing. Realistically, because bioenergy and cattle markets drive April. Annual rainfall was similar across locations for 2010 switchgrass profitability (Rogers et al., 2014; Boyer et al., 2015; (29.4 in at both Spindletop and Eden Shale) and 2011 (53.7 in at Biermacher et al., 2017), optimal management plans will per- Spindletop and 50.2 in at Eden Shale); monthly rainfall totals mit market-based flexibility. In addition, ongoing breeding are reported in Fig. 1. Because of spatial constraints imposed programs present opportunity for continued improvement by concomitant research projects (i.e., we had a limited stand of switchgrass for forage or biomass uses; development of area available for sampling for this project), we elected to

2 of 8 crop, forage & turfgrass management Fig. 1. Monthly rainfall at the Spindletop and Eden Shale farms, 2010 and 2011.

implement a hand-harvest sampling design, rather than a 0.670, rN = 0.971). These data support the use of NIRS to predict larger-scale mechanical harvest system. Each stand was sub- forage quality of switchgrass samples and confirm the robust- divided into four blocks of eleven 4 ft2 sampling areas (2 ft × ness of the NIRS calibration used for this analysis. 2 ft) in a randomized complete block design, with each sam- pling area randomly blocked and assigned a harvest date (one To synthesize biomass and forage quality data, relative for- sampling area from each block was harvested at each harvest age quality (RFQ), digestible dry matter (DDM) yield, and date) for a total of four samples per harvest date. Although crude protein yield were calculated. Digestible dry matter individual sampling plots were small, stands were relatively yield was calculated as %DDM × biomass, and crude protein uniform, and number of tillers per plot tended to be consistent yield was calculated as %CP × biomass. The RFQ was calcu- across replicates. Switchgrass was harvested to 8 in stubble lated based on the following formula: height every 2 weeks beginning in mid-May (11 dates total per year) using a serrated rice knife, folded into a brown paper RFQ = (TDN × DMI)/1.23 bag, and dried in a forced-air oven at 140°F for 3 to 5 days. Dry where TDN is total digestible nutrients (considered equiva- weight was recorded as g m-2 and converted to tons/ac. lent to digestible organic matter) and DMI is dry matter intake, calculated according to the formula DMI = 120 / %NDF. The RFQ reflects both digestibility (from TDN) and intake potential Forage Quality Analysis (from DMI) (Moore and Undersander, 2002). RFQ has been uti- Forage quality analysis was conducted using a switchgrass lized as an indicator of forage quality across a variety of forages, forage quality calibration developed for near-infrared reflec- including grasses (Hancock et al., 2014; Salama and Zeid, 2016). tance spectroscopy (NIRS) at the University of Kentucky (Keene, 2014). This previously developed and calibrated NIRS Switchgrass yield and forage quality data were averaged equation was used to predict neutral detergent fiber (NDF), within year (2010 and 2011) and standardized by accumulated acid detergent fiber (ADF), and % Nitrogen (N). Crude - pro growing degree days (AGGD, Tbase = 50°F). Switchgrass leaf area tein (CP) was calculated based on %N (6.25 × %N = %CP). To index (LAI) was accurately predicted by AGDD in a Nebraska validate the use of this NIRS equation for our project, we study (Mitchell et al., 1998), supporting the use of AGDD for randomly selected 42 samples from our sample set for stan- evaluating seasonal patterns in switchgrass growth and qual- dard wet-lab analysis. Briefly, for this 42-sample validation set, ity. Biomass yield and forage quality parameters for both years %N was calculated by combustion (Nitrogen analyzer model were plotted by AGDD, and quadratic regression was used to FP-528, LECO Corporation, St. Joseph, MI), NDF was analyzed fit a best fit line (SAS 9.3, PROC GLM, SAS Inst. Inc., Cary, NC). by a fiber analyzer (ANKOM model 200; ANKOM Technology Corp., Fairport, NY) method modified from Komarek and Siroi (1993), and ADF was analyzed using the same fiber ana- Seasonal Biomass Accumulation lyzer modified from Van Soest et al. (1991). The NIRS-predicted and Forage Quality results (using the NIRS equation developed and calibrated by Spring greenup was observed in both stands in late April in Keene, 2014) were correlated with wet-lab determined values 2010 and early May in 2011. When biomass trends were stan-

(critical r value, p < 0.05, for n = 42 is 0.312; rADF = 0.946, rNDF = dardized by AGDD, they were similar across years for each crop, forage & turfgrass management 3 of 8 Table 2. Harvest dates for Alamo and Cave-in-Rock switchgrass, with corresponding accumulated growing

degree days (AGGD, Tbase = 50° F) and “weeks after greenup” designation. Maturity stages were recorded for 2011 only. Harvest dates AGDD Weeks after 2010 2011 2010 2011 greenup Alamo CIR† Alamo CIR Alamo CIR Alamo CIR 2 17-May 18-May 19-May 17-May 750 726 663 621 4 1-Jun 2-Jun 2-Jun 31-May 1057 1035 957 878 6 15-Jun 16-Jun 16-Jun‡ 14-Jun‡ 1411 1373 1285 1201 8 29-Jun 30-Jun 30-Jun 28-Jun§ 1784 1741 1599 1499 10 13-Jul 14-Jul 14-Jul§ 12-Jul 2125 2084 1965 1849 12 27-Jul 28-Jul 28-Jul 26-Jul 2529 2484 2373 2246 14 10-Aug 11-Aug 11-Aug 9-Aug 2910 2845 2760 2639 16 24-Aug 25-Aug 25-Aug 23-Aug 3277 3206 3093 2947 18 7-Sep 8-Sep 8-Sep 6-Sep 3585 3511 3380 3267 20 21-Sep 22-Sep 22-Sep 20-Sep 3874 3805 3612 3471 22 5-Oct 6-Oct 6-Oct 4-Oct 4066 3977 3759 3616 † CIR = Cave-in-Rock. ‡ Boot stage. § Early flowering stage.

cultivar. Growth stages were recorded in 2011 (Davis, 2014). suitable for forage. Because our cultivars were planted in Alamo was at the boot stage on June 10, and the early flowering different soils at different sites, we were unable to make stage in early-mid July, while Cave-in-Rock was at boot stage meaningful comparisons between cultivars in this study. We on June 16 and early flowering stage on June 25 (Table 2). recommend additional research to better understand differ- ences in growth and quality patterns among cultivars, with Biomass accumulation rates were similar in Cave-in-Rock cultivars of interest planted in the same sites. and Alamo switchgrass stands through the early part of the season (Fig. 2). At 14 weeks (2800 AGDD), Cave-in-Rock Biomass accumulation trends of Alamo identified in this biomass reached its maximum, while biomass continued study are consistent with the literature—Alamo biomass was to accumulate in the Alamo stand through about 18 weeks greater in October than in July or April in a Tennessee study after green-up (3500 AGDD). For both cultivars, CP declined (Garten et al., 2010). Peak Alamo biomass in this study (8.9 t/ predictably throughout the growing season, leveling out for ac) was similar to that reported by Ashworth et al. (2017) in Cave-in-Rock and for Alamo around weeks 16 to 18 (3200– Arkansas (8.3 t/ac). Declining CP throughout the growing sea- 3500 AGDD) (Fig. 3). The NDF exhibited a consistent positive son is well-established in switchgrass. For example, a study in trend through the end of the growing season in Cave-in-Rock, Oklahoma found that CP of Alamo switchgrass harvested at but plateaued after 16 weeks in Alamo (3200 AGDD) (Fig. 4). vegetative stage was higher than CP in switchgrass harvested The ADF increased consistently through the season in both at boot stage. The lowest CP in that study was in switchgrass cultivars (Fig. 5). The RFQ declined throughout the growing harvested at the end of the season—a typical biomass harvest season in both cultivars, but leveled out in Alamo around (Kering et al., 2013). Similarly, nitrogen removal in Alamo har- week 16 (3200 AGDD) (Fig. 6). The DDM yields in Alamo vested for biomass was highest in early season (May-June), and peaked at week 18 (3400 AGDD), but peaked around weeks 12 declined throughout the rest of the growing season, with min- to 14 (2600 AGDD) in Cave-in-Rock (Fig. 7). Additionally, CP imums in winter-harvested biomass (Ashworth et al., 2017). yields for Alamo peaked at week 14 (2600 AGDD), but peaked Seasonal trends in NDF and ADF in Alamo switchgrass in our around week 12 (2400 AGDD) in Cave-in-Rock (Fig. 8). study were also similar to NDF and ADF trends reported by Kering et al. (2013). Similarly, total nitrogen and nonstructural carbohydrates declined and lignin and cellulose increased Biomass and Forage Quality through the growing season in both Cave-in-Rock and Alamo Trends in Context in an Iowa study (Aurangzaib et al., 2016). Alamo, a coarse-stemmed lowland cultivar, is known for its high biomass and is consequently frequently planted The CP was higher in Cave-in-Rock early in the season because for biomass applications. In contrast, Cave-in-Rock is a of lower biomass allocation to structural fiber consistent with finer-stemmed upland cultivar that typically accumulates the upland cultivar. Cave-in-Rock biomass production was less biomass, especially in a one-harvest system. In general, moderate and primarily early-season (5–7 t/ac). Low biomass upland cultivars are considered more suitable for forage accumulation in late-season Cave-in-Rock could be related applications, while lowland cultivars are considered less to low leaf retention and/or earlier reproductive maturity. In

4 of 8 crop, forage & turfgrass management Fig. 2. Biomass accumulation in Alamo and Cave-in-Rock switchgrass during the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD).

Fig. 3. Crude protein of Alamo and Cave-in-Rock switchgrass harvested throughout the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD).

Fig. 4. Neutral detergent fiber (NDF) of Alamo and Cave-in-Rock switchgrass harvested throughout the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD).

contrast, while Alamo allocated biomass to structural fiber in N contamination during cellulosic fermentation for liquid early season growth, leaf production and retention appeared fuels (Aurangzaib et al., 2016). higher in late season growth compared to Cave-in-Rock, lead- ing to higher late season CP in Alamo than Cave-in-Rock. High CP is important in switchgrass harvested for forage to Implications for Management produce higher livestock gains, but lower CP is desirable in This research supports the use of switchgrass for flexible switchgrass harvested for biomass because less risk of harm- multipurpose plantings. They can be harvested early when ful nitrous oxide emissions when co-firing with coal and less forage quality is high, or permitted to grow all season and crop, forage & turfgrass management 5 of 8 Fig. 5. Acid detergent fiber (ADF) of Alamo and Cave-in-Rock switchgrass harvested throughout the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD).

Fig. 6. Relative forage quality (RFQ) of Alamo and Cave-in-Rock switchgrass harvested throughout the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD).

Fig. 7. Digestible dry matter (DDM) yield of Alamo and Cave-in-Rock switchgrass harvested throughout the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD).

harvested once in late season for biomass. While reduced Lemus et al., 2014). Importantly, development of management stand longevity under two-harvest management is well recommendations for dual-use switchgrass stands need not documented (e.g., Parrish and Fike, 2005), other studies rely on a two-harvest system. Instead, an appropriate variety have demonstrated consistent yields under a two-cut system (i.e., one that demonstrates stand longevity under two-har- over nearly a decade (Olson et al., 2009; Lemus et al., 2014), vest systems and acceptable early-season forage quality and suggesting that stand longevity in some cultivars can be late-season biomass) could be grown for its flexibility. Rather maintained under a two-cut system when combined with than growing out a single-use variety and depending on a more intensive maintenance techniques (Fike et al., 2006a, b; biomass market, a more flexible variety could be marketed

6 of 8 crop, forage & turfgrass management Fig. 8. Crude protein yield of Alamo and Cave-in-Rock switchgrass harvested throughout the 2010 and 2011 growing seasons in central Kentucky, standardized by accumulated growing degree days (AGDD). as a summer hay or, if the summer hay market is poor, har- References vested at the end of the season for biomass. Ashworth, A.J., A.C. Rocateli, C.P. West, K.R. Brye, and M.P. Popp. 2017. Switchgrass growth and effects on biomass accumulation, moisture content, and nutrient removal. Agron. J. 109:1359–1367. In the Southeast, when biomass production is the primary use doi:10.2134/agronj2017.01.0030 of a switchgrass stand, lowland cultivars such as Alamo are Aurangzaib, M., K.J. Moore, S.V. Archontoulis, E.A. Heaton, A.W. recommended because they continue to accumulate biomass Lenssen, and S. Fei. 2016. Compositional differences among for much of the growing season. Lowland cultivars planted at upland and lowland switchgrass ecotypes grown as a bioenergy feedstock crop. Biomass Bioenergy 87:169–177. doi:10.1016/j.biom- higher latitudes delay flowering, remaining in vegetative state bioe.2016.02.017 longer and potentially producing more biomass compared to Biermacher, J.T., M. Haque, J. Mosali, and J.K. Rogers. 2017. Economic lowland cultivars planted at lower latitudes (Casler and Boe, feasibility of using switchgrass pasture to produce beef cattle gain 2003). However, lowland cultivars can be limited by winter and bioenergy feedstock. BioEnergy Res. 10:740–749. doi:10.1007/ temperatures at higher latitudes. While the Alamo stand used s12155-017-9835-6 in this study has been successfully maintained since its estab- Boyer, C.N., A.P. Griffith, D.W. McIntosh, G.E. Bates, P.D. Keyser, and B.C. English. 2015. Breakeven price of biomass from switchgrass, lishment in 2007, an Alamo stand planted at the same location big bluestem, and Indiangrass in a dual-purpose production as part of a variety trial in 2001 experienced significant die- system in Tennessee. Biomass Bioenergy 83:284–289. doi:10.1016/j. back due to winterkill in 2004 (Olson et al., 2009). Thus, both biombioe.2015.10.006 environmental and economic considerations should be taken Casler, M., and A. Boe. 2003. Cultivar × environment interactions in switchgrass. Crop Sci. 43:2226–2233. doi:10.2135/cropsci2003.2226 into consideration when selecting varieties for planting for Davis, D.H. 2014. Evaluating the effect maturity on the intake and either single- or dual-use systems (Hong et al., 2014). digestibility of switchgrass hay consumed by beef steers. Thesis, University of Kentucky. Lexington, KY. Our results are consistent with the literature with respect to Delaquis, E., R. Samson, P. Seguin, A. Mustafa, and H. Martel. 2014. biomass accumulation and forage quality patterns through- Impacts of improved switchgrass and big bluestem selections on yield, morphological characteristics, and biomass quality. out the growing season. These trends will aid in making Advances in Agriculture. 2014:1–14. doi:10.1155/2014/192824 decisions for management of switchgrass for biomass and/ Fike, J.H., D.J. Parrish, D.D. Wolf, J.A. Balasko, J.T. Green, Jr., M. Ras- or forage in the southeast. We recommend similar studies nake, and J.H. Reynolds. 2006a. Long-term yield potential of in other regions where switchgrass may be a viable bioen- switchgrass-for-biofuel systems. Biomass Bioenergy 30:198–206. ergy and/or forage crop, to aid in generating robust regional doi:10.1016/j.biombioe.2005.10.006 trends for biomass and forage quality. These studies could Fike, J.H., D.J. Parrish, D.D. Wolf, J.A. Balasko, J.T. Green, M. Rasnake, and J.H. Reynolds. 2006b. 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