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Published online 1 February 2006
Published in Crop Sci 46:712-720 (2006)
© 2006 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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FORAGE & GRAZINGLANDS

Management of Switchgrass-Dominated Conservation Reserve Program Lands for Biomass Production in South Dakota

V. R. Mulkeya, V. N. Owens*,b and D. K. Leeb

a 7049 Grayson Turnpike, Speedwell, VA 24374
b Plant Science Dep., South Dakota State University, 247 NPB, Box 2140-C, Brookings, SD 57007-2141

* Corresponding author (vance.owens{at}sdstate.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Switchgrass (Panicum virgatum L.) has been planted on land enrolled in the Conservation Reserve Program (CRP). Management strategies for conversion of this land from CRP to biomass energy require evaluation. Objectives of this study were to: (i) determine the effect of harvest timing and N rate on biomass production and characteristics of switchgrass land enrolled in or managed similarly to CRP and (ii) evaluate the impact of harvest management on species composition and persistence. Five N rates (spring applications of 0, 56, 112, and 224 kg ha–1 and 224 kg ha–1 split between spring and postharvest) and two harvest timings (anthesis and post-killing frost) were applied to plots from 2001 to 2003 at three South Dakota locations. Harvesting after a killing frost produced higher total yields and improved switchgrass persistence compared with anthesis harvests. The concentration of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) increased between anthesis and killing-frost harvests, while total nitrogen (TN) and ash decreased. Nitrogen applied at 56 kg ha–1 increased total biomass without affecting switchgrass persistence, but there was no additional benefit with N above 56 kg ha–1. Harvesting long-established switchgrass stands once per year after a killing frost and applying N at 56 kg ha–1 was an effective system for switchgrass biomass production and persistence on land enrolled in or managed similarly to CRP in South Dakota.


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
BIOMASS is a renewable resource that can be used to generate electricity, heat, or liquid fuels such as ethanol. A successful perennial grass-based bioenergy system requires reliable establishment and persistence, knowledge of optimum cultural and production practices, high yielding cultivars, and appropriate conversion technology. The Conservation Reserve Program (CRP) is a land retirement program established by the Food Security Act of 1985. The main objectives of this program are to reduce soil erosion, reduce commodity surpluses, and to supplement farm income (Jewett et al., 1996). Native warm-season grasses such as switchgrass are permitted for use as permanent vegetation on CRP land. Rather than losing the environmental benefits and converting switchgrass CRP land to traditional crops when contracts expire, the herbaceous material could be used as a biomass feedstock.

Switchgrass can produce up to 14 Mg dry matter (DM) ha–1 in parts of the USA, more than 60% of which is lignocellulose, which contains the desirable components for biomass energy (Vogel and Masters, 1998). At similar stages of maturity warm-season grasses such as switchgrass have higher lignocellulose concentrations than cool-season grasses and legumes (Reid et al., 1988) and, thus, are well suited as biomass feedstocks. In addition, lignocellulose concentrations increase as switchgrass matures primarily as a result of a decrease in the leaf-to-stem ratio (Griffin and Jung, 1983; Twidwell et al., 1988).

Switchgrass is sensitive to frequent defoliation because it elevates the apical meristems above ground during early vegetative development. New growth occurs from crown buds or aerial axillary meristems, and it has a high ratio of reproductive to vegetative tillers early in the growing season (Mitchell et al., 1998; Sanderson et al., 1999). Harvesting monoculture stands of switchgrass three times per year reduced yields by 51% as a result of reduced photosynthetic surface area on frequently defoliated plants (Cuomo et al., 1998). In the Midwest, Vogel et al. (2002) recommended harvesting switchgrass at the R3 to R5 stage of maturity (panicle fully emerged from boot to anthesis) to maximize biomass yields and allow sufficient regrowth to occur such that in years with adequate precipitation a second harvest (after a killing frost) may be obtained. Monoculture switchgrass cut once annually for 2 yr at anthesis, anthesis plus 3 wk, or anthesis plus 6 wk, produced average yields of 7.5, 7.3, and 8.6 Mg ha–1, respectively, while plots harvested two times per year (at anthesis and after a frost) produced lower yields (6.5 and 1.0 Mg ha–1, respectively) (Balasko et al., 1984).

Switchgrass efficiently uses nitrogen and phosphorus (Vogel et al., 2002). Yearly nitrogen application up to 150 kg ha–1 resulted in an average yield increase of 15 kg DM kg–1 N applied (Berg, 1995). Others have also noted an increase in yield (Hall et al., 1982; George and Obermann, 1989; Madakadze et al., 1999) and TN (Jung et al., 1990; Brejda et al., 1995) in response to applied N to warm-season grasses.

Despite the potential for biomass production of switchgrass enrolled in CRP, data related to harvest and N management of this resource are lacking. Therefore, the objectives of this study were to: (i) determine the effects of harvest timing and N rate on yield and biomass characteristics of long-established switchgrass stands enrolled in or managed similarly to CRP and (ii) evaluate the impact of harvest management on species composition and persistence in these stands.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This research was conducted at three locations in South Dakota. Location 1, in Moody County (96°41' W; 44°10' N), is a Wentworth–Egan soil (fine-silty, mixed, mesic Udic Haplustolls) with a 2 to 6% slope. Age of stand was 13 yr in 2000. Location 2, in Marshall County (97°20' W; 45°50' N), is situated on Buse (fine-loamy, mixed, frigid Typic Calciudolls) with a 6 to 9% slope. Age of stand was 12 yr in 2000. Location 3 is located in Gregory County (99°45' W; 43°43' N) on a Ree loam (fine-loamy, mixed, mesic Typic Argiustolls) with no slope. Age of stand was 9 yr in 2000. Locations 1 and 2 were enrolled in CRP while Location 3 has been managed for wildlife habitat (similar to CRP) since establishment. Detailed records for years in which these stands were harvested for hay (emergency CRP release on CRP land) or burned were unavailable; however, to our knowledge none of the herbage from any of the locations was routinely removed during the stand life. These sites were selected in 2000 and mowed at a 10- to 15-cm height in the autumn before imposing treatments in 2001. Selected soil chemical and physical properties in the top 15 cm for each location are shown in Table 1. Phosphorus (2.5 g m–2) was broadcast across the entire experimental area at each location during spring 2001 to bring soil fertility to recommended levels.


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  		Table 1. Selected soil chemical and physical properties in top 15 cm for three switchgrass locations in South Dakota at initiation of research in 2001.

 
The experimental design was a factorial arrangement of two harvest dates and five N rates within a randomized complete block with four replicates. Plots 1.9 m wide and 6.1 m long were harvested once per year in 2001, 2002, and 2003 at anthesis or post-killing frost. Five levels of N fertilization consisted of a spring application of 0, 56, 112, and 224 kg ha–1 and split application of 224 kg ha–1(one-half applied in spring and the other half applied after the anthesis or killing-frost harvests). The nitrogen source was ammonium nitrate, which was preweighed and hand-broadcast onto each plot on the dates shown in Table 2.


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  		Table 2. Nitrogen application and harvest dates for three switchgrass locations in South Dakota in 2001, 2002, and 2003. Stand age in 2000 was 25, 12, and 9 yr for Locations 1, 2, and 3, respectively.

 
All locations were treated with herbicides as needed to help control broadleaf and grassy weeds. In 2003, glyphosate [N-(phosphonomethyl) glycine] was applied on 12 May at Location 1, 2,4-D amine [isooctyl (2-ethylhexyl) ester of 2,4-dichlorophenoxyactic acid] and atrazine (2-chloro-4-ethylamine-6-isopropylamino-s-triazine) were applied 12 May at Location 3, and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid, monethanolamine salt) was applied 12 June at Location 2.

Yield was determined from a 1.1-m-wide by 4.8-m-long swath through the center of each plot with a sickle bar mower at a cutting height of 10 to 15 cm on the dates listed in Table 2. One 0.19-m2 subsample was hand-clipped from each plot before mowing for the anthesis and killing-frost harvests in 2001 and anthesis harvest in 2002. Two 0.19-m2 subsamples per plot were taken at all successive harvests. Subsamples were frozen at 0°C and then separated into categories of switchgrass, grassy weeds, broadleaf weeds, senesced material, and miscellaneous. Senesced material consisted predominately of dead plant fragments while the miscellaneous category was primarily unidentifiable green plant fragments. Yellow sweetclover (Melilotus officinalis Lam.) was also a category in 2002 at Location 2 because of its abundance relative to other undesirable species. Fractionated subsamples were weighed, dried at 60°C for 48 h in a forced-air oven, and reweighed to determine dry matter yield and species composition. After drying, individual components were recombined for grinding and subsequent quality analysis. Dried samples were ground in a Wiley mill (Thomas-Wiley Mill Co., Philadelphia, PA) to pass a 1-mm screen and then reground to uniformity in a Udy-cyclone impact mill with a 1-mm screen.

Concentrations of NDF, ADF, ADL, and TN were predicted for all forage samples by near infrared reflectance spectroscopy (NIRS) (NIRS Model 5000, Foss NIRSystems, Silver Springs, MD) on the basis of a calibration data set of 174 (20%) samples representing all harvest years (Garcia-Ciudad et al., 1993). A set of 30 samples was used for cross-validation. Calibration and validation statistics were generated by WinISI (Version 1.5) system software (Infrasoft International LLC., State College, PA). Prediction equations had standard errors of calibration of 0.8, 22.6, 14.6, and 5.7 g kg–1, standard errors of cross validation of 1.1, 24.7, 16.7, and 6.6 g kg–1, and coefficients of determination of 0.98, 0.92, 0.93, and 0.90 for TN, NDF, ADF, and ADL, respectively. Values for 1 – V/R (where V/R is the ratio of enexplained variance to total variance) were 0.96, 0.91, and 0.87 for TN, NDF, ADF, and ADL, respectively. Neutral detergent fiber and ADF were determined with an Ankom200 Fiber Analyzer (ANKOM Technology Corp., Fairport, NY) (Anonymous 2003a, 2003b). Lignin analysis was determined with a Daisy Incubator II Digestor (ANKOM Technology Corp., Fairport, NY) (Anonymous, 2002). Total N was quantified with a Vario Max CNS elemental analyzer (Elementar Instrument, Mt. Laurel, NJ). Ash concentrations were determined by the methods described by Undersander et al. (1993).

Statistical Analysis
Yield and quality data were analyzed by analysis of variance (ANOVA) using PROC MIXED in SAS (Littell et al., 1996). A least significant difference (LSD) was used to separate means when the appropriate F test was statistically significant (P = 0.05). Nitrogen rate (N rate), harvest timing (HT), and harvest year (HY) were considered to be fixed effects while replication was treated as random. Species composition was analyzed using PROC MIXED of repeated measures in SAS (Littell et al., 1996; Rao, 1998), and a LSD (P = 0.05) was used to separate mean effects when the appropriate F test was significant.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Yield
Below normal precipitation significantly affected yield at all locations but was especially apparent at Location 3 in 2002 when annual precipitation was more than 44% (291 mm) below the 30-yr average (Table 3). There was a significant harvest timing x harvest year interaction for total yield at all locations and for switchgrass yield at Locations 1 and 2 (Table 4). At Location 1, total biomass at anthesis declined significantly from 2001 to 2002, but there was no significant difference between harvest years at the killing frost harvest (Fig. 1 ). Total yield at Location 1 was significantly higher in 2003 than 2001 and 2002 at the killing frost harvest, but the opposite was true at the anthesis harvest where total yields in 2003 were lower than 2001. Switchgrass production at Location 1 followed a pattern similar to total yield. However, yield of switchgrass harvested at anthesis declined more than total yield between 2001 and 2002, which was due to the negative influence of annual anthesis harvests on switchgrass persistence.


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  		Table 3. Mean temperature and precipitation data for three switchgrass locations and harvest years (Todey, 2005).

 

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  		Table 4. Analysis of variance (ANOVA) and probability values for total yield (TY), switchgrass yield (Swg), total nitrogen (TN), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and ash at three locations for 3 yr in South Dakota.

 

Figure 1
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  		Fig. 1. Harvest timing x harvest year interaction for total yield (TY) and switchgrass yield (Swg) at anthesis (An) and killing-frost (KF) harvests at three locations in South Dakota. Values are averaged across N rate. Fisher's protected LSD(0.05) values, to compare across harvest timing and harvest year, are shown above the respective bars for TY and Swg yield for each location. NS = not significant at 0.05 level of probability.

 
Switchgrass harvested after a killing frost was less negatively affected by below normal precipitation or annual harvests during the 3-yr period. At Location 2 total biomass was highest in 2002 at both the anthesis (3541 kg ha–1) and killing-frost (5457 kg ha–1) harvests despite lower than average rainfall, but switchgrass yields in 2002 were similar to or lower than other years (Fig. 1). Production at Location 2 was significantly affected by yellow sweetclover growth in 2002 when it represented nearly 17% of the total harvested biomass. This resulted in higher total yields even with reduced precipitation (37% below normal) but tended to reduce the switchgrass yield component, particularly at the anthesis harvest. In addition, switchgrass yields declined from 2001 to 2003 when harvested at anthesis, whereas they increased when harvested after a killing frost during the same time period at this location. Therefore, despite the effect of sweetclover encroachment in 2002, the reduction in switchgrass yield was also due to a significant reduction in switchgrass persistence in anthesis-harvested plots compared with those harvested after a killing frost (Table 5). Location 3 was severely affected by reduced precipitation (44% below normal) in 2002, especially at anthesis when total and switchgrass production declined 4493 and 3698 kg ha–1, respectively, from 2001 (Fig. 1).


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  		Table 5. Analysis of variance (ANOVA) and probability values for percentage switchgrass (Swg), grassy weeds (GW), broadleaf weeds (BW), senesced material (SM), miscellaneous (Misc.), and sweetclover (SC) for three locations over 3 yr in South Dakota.

 
Dry matter yields have been reported to decline between anthesis and a killing frost because of leaf senescence and loss (Taylor and Allinson, 1982). However, Casler and Boe (2002) compared single annual harvests in August and October over a period of 4 yr and found that switchgrass persistence, and thus yield, declined more rapidly in the August than the October harvest. In the current research, total production at killing frost harvests has remained similar to or exceeded that obtained at anthesis. With the exception of Location 2 in 2001, switchgrass yields were always significantly higher at the killing-frost than the anthesis harvest (Fig. 1). Two factors may be involved in increased total or switchgrass biomass by harvesting after a killing-frost compared with anthesis: (i) although we attempted to harvest plots when the majority of reproductive culms had reached anthesis, some were obviously less mature; therefore, maximum production may not have been reached by the indicated anthesis harvest dates; and (ii) switchgrass persistence began to decline significantly (Table 5) after the first harvest season in plots harvested at anthesis, while there has been no measurable effect of the killing-frost harvest on switchgrass persistence over the 3-yr period. A noticeable reduction in the switchgrass sward was apparent in anthesis plots with 0 N applied between 2001 and 2002, with further visible stand decline in 2003 at all locations. Although Casler and Boe (2002) noticed a decline in switchgrass persistence after 3 to 4 yr, it appears that long-established switchgrass, such as that enrolled in CRP, may actually be more sensitive to harvest timing than younger switchgrass stands.

A N fertilizer rate up to 112 kg N ha–1 increased total biomass by a minimum of 30% at all locations (Fig. 2 ). Despite a similar trend, yields of the switchgrass component were not significantly different among treatments at any location. George et al. (1990) reported a 61% increase in switchgrass yield from May to June when 90 kg N ha–1 was applied. Several other studies have also shown an improvement in switchgrass production with N application (Balasko and Smith, 1971; George et al., 1995; Vogel et al., 2002). Typically, warm-season grasses do not produce significantly higher yields with N rates above 120 kg ha–1, and recommended N rates for switchgrass in the Central Plains and Midwest states ranges from 50 to 120 kg ha–1 (Brejda, 2000). However, in the three environments tested in South Dakota where switchgrass was ≥9 yr old in 2000, we did not detect a significant switchgrass yield response to N despite the fact that total biomass was higher with applied N. On the basis of low initial soil NO3–N levels at each location, we anticipated a greater switchgrass response to applied N. However, since switchgrass at these locations has probably not been removed more than 50% of the past 10 or more years, soil organic carbon (SOC) concentrations, particularly at Locations 1 and 2, were very high (Table 1). We speculated that mineralization of SOC may have released sufficient N for switchgrass (a species inherently N-use efficient) production in control plots such that yield in these plots was similar to those to which N was applied. The effect of accumulated SOC and subsequent mineralization may not provide sufficient N for optimal and long-term switchgrass production in an annual harvest system, however.


Figure 2
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  		Fig. 2. Nitrogen rate effect on total yield (TY), and switchgrass yield (Swg) at three locations in South Dakota. Values are averaged across harvest timing and harvest year. Fisher's protected LSD(0.05) values, to compare across N rate are shown above the respective bars for TY and Swg yield for each location. NS = not significant at 0.05 level of probability.

 
Species Composition
At Location 2 there was a significant harvest timing x harvest year interaction for switchgrass, grassy weeds, senesced material, miscellaneous, and sweetclover; however, for all locations, harvest timing had the greatest and most consistent effect on percentage switchgrass in the stand (Table 5). Averaged across harvest year and N rate, switchgrass made up 54, 32, and 56% of the stand at anthesis and 77, 52, and 79% after a killing frost at Locations 1, 2, and 3, respectively (Fig. 3 ). While the switchgrass component increased, the proportion of grassy and broadleaf weeds tended to decrease in plots harvested after a killing frost. Delaying harvest until after a killing frost increases the length of canopy cover in a stand. Sanderson (2000) noted that harvesting forage once a year may result in increased standing forage, thus reducing the amount of light intercepted at the base of the plant canopy. Forage response to altered light quality may result in elongation of the stem and leaves and decreased tillering which may in turn reduce stand density and persistence. On the other hand, switchgrass was nearly eliminated after 6 yr in a study in which it was harvested once, twice, or three times annually because it tends to be sensitive to frequent defoliation as well (Sanderson, 2000). In the current study on long-established stands, switchgrass persistence has declined rapidly when harvested annually at anthesis.


Figure 3
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  		Fig. 3. Harvest timing effect on switchgrass (Swg), grassy weeds (GW), broadleaf weeds (BW), senesced material (SM), and miscellaneous (Misc.) percentage at three locations in South Dakota, and sweetclover (SC) for Location 2. Values are averaged across N rate and harvest year. Fisher's protected LSD(0.05) values, to compare across harvest timing are shown above the respective bars for each component for each location. NS = not significant at 0.05 level of probability.

 
Harvest year significantly affected switchgrass percentage at all locations (Table 5). The highest switchgrass percentage occurred in 2001 at Locations 1 and 3 and in 2003 at Location 2 (Fig. 4 ). Switchgrass percentage was lowest in 2002 at Location 1 and 3 as a result of below normal precipitation (Table 3) and subsequent reductions in switchgrass growth. Switchgrass percentage increased in 2003 to levels comparable to those in 2001 at both Locations 1 and 3. At Location 2, switchgrass composition was highest in 2003, probably a result of better weed control. Competition from other grassy and broadleaf weeds was also a factor in switchgrass decline, but was more apparent in plots harvested at anthesis than in those harvested after a killing frost (Fig. 3).


Figure 4
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  		Fig. 4. Harvest year effect on switchgrass (Swg), grassy weeds (GW), broadleaf weeds (BW), senesced material (SM), and miscellaneous (Misc.) percentage for three locations in South Dakota, and sweetclover (SC) for Location 2. Values are averaged across N rate and harvest timing. Fisher's protected LSD(0.05) values, to compare across harvest year, are shown above the respective bars for each component for each location. NS = not significant at 0.05 level of probability.

 
Biomass Quality
There was a significant N rate x harvest year interaction for TN at Locations 1 and 2 (Table 4). At Location 1, the concentration of TN increased significantly with increasing N rate during 2002 and 2003 but not in 2001 (Fig. 5 ). The TN concentration of biomass from plots receiving the 0 kg N ha–1 treatment decreased from 2001 to 2002 then increased in 2003, while all other N rates resulted in either equal or greater biomass TN concentrations each consecutive harvest year at Location 1. The year-to-year increase in TN concentration of harvested material was not noted at either of the other two locations. At Location 2 the highest TN concentration for all N rates occurred during the 2002 harvest year, which may be related to sweetclover encroachment. Legumes have a greater concentration of TN in their stems and leaves than grasses; therefore, they may significantly increase TN concentration of a stand if present in significant quantities (Posler et al., 1993).


Figure 5
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  		Fig. 5. Nitrogen rate x harvest year interaction for total nitrogen (TN) concentration from biomass harvested from three locations in South Dakota. Values are averaged across harvest timing. Fisher's protected LSD(0.05) values, to compare across N rate and harvest years, are shown above the respective bars for each location. NS = not significant at 0.05 level of probability.

 
Increasing N rates up to 224 kg ha–1 typically resulted in greater TN concentrations at all locations (Fig. 5). However, TN concentration actually declined with increasing N at Location 2 in 2001. The reason for the negative relationship between N rate and biomass TN concentration at Location 2 is not clear. The effect of N rate was consistent across years at Location 3, where TN concentration increased with increasing N and average yields (switchgrass and total) followed similar patterns. The 224 kg N ha–1 split application treatment resulted in TN concentrations similar to or greater than the 112 kg N ha–1 application rate at all locations. Although not significantly different, utilizing a 224 kg N ha–1 split N application resulted in TN concentrations numerically higher than a single application of the same amount at Locations 1 and 3 in 2 of 3 yr (Fig. 5). The opposite was true at Location 2, where cool-season species seemed to be favored competitively with the one-time application of 224 kg N ha–1, particularly in 2002.

There was a significant harvest timing x harvest year interaction for TN at all locations (Table 4), primarily a result of greater variation in TN concentration at the anthesis compared with the killing-frost harvest. The average decrease in TN concentration between the anthesis and killing-frost harvests was 7.3, 7.7, and 4.8 g kg–1 at Locations 1, 2, and 3, respectively, (Table 6). Seasonal decline in TN concentrations in switchgrass has been well documented (Griffin and Jung, 1983; Twidwell et al., 1988). The rate of nutrient decline is affected by environmental factors such as light, temperature, and drought stress and is a result of a decrease in leaf-to-stem ratio, senescence of leaves, and decline in stem quality (Griffin and Jung, 1983). In addition, by delaying harvest until after a killing frost, much of the N within the plant may be remobilized to roots and other storage organs for winter survival (Owensby et al., 1970; Vogel et al., 2002), resulting in a possible reduction in the need for N inputs and an increase in the concentration of lignocellulose for biomass conversion processes.


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  		Table 6. Means and LSD (0.05) values for total nitrogen (TN), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and ash for harvest timing (HT), harvest year (HY), and harvest timing x harvest year interaction for total biomass production at three locations over 3 yr in South Dakota. Values are averaged across N rate.

 
There was a significant harvest timing x harvest year interaction for NDF and ADF at Location 3 (Table 4). On average however, delaying harvest until after a killing frost had a greater impact on NDF and ADF concentrations than harvest year (Table 6). Averaged across locations and years, NDF and ADF increased 76 and 51 g kg–1, respectively, between anthesis and killing frost. Jung and Vogel (1992) reported that NDF concentrations increased a minimum of 68 and 85 g kg–1 DM in switchgrass leaves and stems, respectively, as harvest was delayed from the vegetative to heading growth stage. Griffin and Jung (1983) found that leaf NDF concentrations changed little with maturity, but NDF in stem tissue increased an average of 115 g kg–1 between the vegetative and early head emergence stages of maturity.

Acid detergent lignin (ADL) was significantly lower for all anthesis harvests than for killing-frost harvests at all locations (Table 4). Averaged across harvest year and N rate, ADL concentrations increased by 15.9, 7.5, and 5.5 g kg–1 between anthesis and killing frost at Locations 1, 2, and 3, respectively (Table 6). Lignin concentrations have been shown to rapidly increase in switchgrass stem tissue with maturation (Jung, 1989; Jung and Vogel, 1992). Griffin and Jung (1983) found that lignin concentration went from 39 to 45 g kg–1 in leaves and from 55 to 85 g kg–1 in stems between the early-leaf emergence and post-anthesis stage of maturity.

Ash concentration decreased from the anthesis to the killing-frost harvest (Table 6). Components of ash can combine with sulfur to produce corrosive sulfates, resulting in slag deposits on biomass equipment, thus reducing efficiency and increasing maintenance costs (McLaughlin et al., 1996). Silica, one component of ash, is lowest in grass stems and highest in leaves; therefore, harvesting forage with a high stem content improves biomass quality for combustion purposes, gives lower silica levels, and increases cellulose content (Samson and Mehdi, 1998).

A N rate x harvest year interaction was significant for ash concentrations at Location 2 (Table 4). At this location ash tended to decrease with increasing N in 2001 and 2003, but increased with N application in 2002 (data not shown). In 2002, significant levels of sweet clover encroachment occurred which probably contributed to the increased ash concentrations at this location, since legumes tend to have higher amounts of ash than grasses (Posler et al., 1993).


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
On the basis of our results, we recommend harvesting switchgrass once per year after a killing frost and applying low to moderate amounts of N (<112 kg N ha–1) to optimize biomass energy production in South Dakota, and potentially in areas of the northern Great Plains with similar environments.


   ACKNOWLEDGMENTS
 
Special appreciation is extended to the following for help with this research: Cuirong Ren and Paul Evenson for statistical advice and Chris Lee and Eva Omdahl for techincal assistance.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This research was funded in part by the South Dakota Agric. Exp. Stn., the U.S. Dep. of Energy through contract DE-FC36-02G012028, A000 with the Great Plains Institute for Sustainable Development, Minneapolis, MN, and the U.S. Dep. of Energy through contract DE-A105-900R2194 with Oak Ridge National Laboratory (ORNL). ORNL is managed by UT-Battelle, LLC, for the U.S. Dep. of Energy under contract DE-AC05-00OR22725. South Dakota Agric. Exp. Stn. Journal Series No. 3490.

Received for publication April 21, 2005.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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The SCI Journals Agronomy Journal Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome