ISRN AgronomyVolume 2012 (2012), Article ID 607476, 7 pagesdoi:10.5402/2012/607476

Research Article

Yield, Yield Distribution, and Forage Quality of Warm-Season Perennial Grasses Grown for Pasture or Biofuel in the Southern Great Plains

James K. Rogers, Frank J. Motal, and Jagadeesh Mosali

Agricultural Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA

Received 28 October 2011; Accepted 20 November 2011

Academic Editors: M. Diaz Ravina, T. E. Fenton, B. Kindiger, and J. Ransom

Copyright © 2012 James K. Rogers et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Fifteen introduced and native warm-season perennial grasses were evaluated for yield, yield distribution, and quality in south-central Oklahoma. These grasses have production potential for forage and/or biofuel. Each was harvested one to four times per year. “Alamo” switchgrass (Panicum virgatum) had a two-year average dry matter yield of 17690 kg . Over 1/3 of this production occurred in May with a crude protein (CP) range of 97–115 g . Alamo’s high yield potential and early spring growth make it attractive for spring forage production and fall biomass production. Other grasses with two-year average dry matter yields over 11200 kg  and 1/3 of yearly production occurring early in the growing season that have potential dual purpose use include “Selection 75” kleingrass (Panicum coloratum), “Midland 99” bermudagrass (Cynodon dactylon), johnsongrass (Sorghum halepense), “Carostan” flaccidgrass (Pennisetum flaccidum), and “Ermelo” weeping lovegrass (Eragrostis curvula).

1. Introduction

Beef cattle production is a major agricultural enterprise in south-central Oklahoma and the southern Great Plains. Large acreages are currently established in both native and introduced warm-season perennial grasses that support beef cattle production. According to the 2007 Census of Agriculture, Oklahoma ranks fifth nationally in cattle and calves and fourth in acres in forage, while Texas ranks number one in both of these categories. The Energy Independence and Security Act of 2007 calls for 136 billion liters of biofuels to be produced from renewable resources in the US by 2022 with just under half to be produced from a cellulosic biomass source such as switchgrass [1]. To meet the demand for cellulosic ethanol production called for in The Energy Independence and Security Act of 2007, could require the conversion of acreage currently established in perennial grasses to higher biomass producing grass species such as switchgrass. There is currently an economic incentive for producers to maintain their production practices in beef cattle; however, to reach the biofuel production goals stated in the Energy Independence and Security Act, with continued emphasis on the use of switchgrass as the primary source of renewable biofuel stock a shift from current grass production systems to switchgrass production may be required. Producers may be willing to shift production practice if they understand that what they grow for biofuel could also be used for forage production to support grazing or haying.

The objective of the study was to evaluate differences in biomass production of fifteen warm-season perennial grasses that are currently grown or have the potential to be grown in Oklahoma, Texas, and other regions and compare their biomass production to the switchgrass variety “Alamo” which is currently used as an industry standard for biomass production for biofuel. A second objective of the study was to determine the distribution of yield of these grasses and identify if opportunities exist for both forage and biofuel production. A third objective was to compare the seasonal quality of these grasses.

2. Materials and Methods

2.1. Species

Native grass species in this study were two switchgrass cultivars, “Alamo” and “Blackwell” and “Lometa” indiangrass (Sorghastrum nutans). Switchgrass is an indigenous species that can be found growing over the eastern two-thirds of the US, Central America, and southern Canada [2]. “Alamo” switchgrass is a “lowland” ecotype released by the Texas A&M experiment station and the Natural Resources Conservation Service (NRCS) in 1978 [3]. In general, lowland switchgrass is taller, leaves are coarser, and they tend to be more rust resistant than their upland counterpart. Lowland switchgrass can have a very strong bunch-type growth habit if left unharvested and tends to be very rapidly growing. Lowland switchgrass is often found on floodplains and similar areas with high-moisture availability [4]. “Blackwell” is an “upland” ecotype switchgrass developed from a selection from seed harvested in 1934 from a single plant growing in a native prairie near Blackwell, OK, USA. It is of medium height and was released in 1944 cooperatively by the Kansas State Experiment station and NRCS plant materials center at Manhattan, KS, USA [5]. Upland switchgrass ecotypes can be found in upland areas that are not subject to flooding [4]. Though shorter and not as rapidly growing, uplands tend to be more cold tolerant and are often found as a component of the native grass prairies in more northern latitudes [6]. “Lometa” indiangrass is a variety released in 1981 by Texas A&M Experiment Station and NRCS plant materials center at Knox City, TX, USA [3] originating from selections near Lometa, TX, USA. Indiangrass has a bunch growth habit with short rhizomes. Its spring growth initiation is similar to switchgrass; however; it exhibits a later maturity than switchgrass [4].

The remaining entries in the study were introduced grasses. “Common” blue panicgrass (Panicum antidotale) is a rhizomatous bunchgrass native to southern Asia [7]. “Common” Dallisgrass (Paspalum dilatatum) is native to South America and is a weak bunchgrass with short rhizomes. “Ermelo” weeping lovegrass was developed from a South African strain and released by the Texas Research Foundation [8]. “Morpa” weeping lovegrass was released by the Oklahoma Agricultural Experiment Station and USDA, ARS. [8].Weeping lovegrass is a strong bunchgrass and well adapted to sandy soils with low water-holding capacity [7]. “Carostan” flaccidgrass was released by the North Carolina Agricultural Experiment Station in 1987. Flaccidgrass is native to central Asia, and it has been grown successfully along the east coast, Arkansas, New Mexico, and Oklahoma [9]. “Common” johnsongrass is a native of North Africa, South Asia, and southern Europe and was introduced into the US around 1830 [10]. It is very adapted to clay soils and can be an aggressive invader. Under close continuous grazing, johnsongrass stands become less vigorous [11]. “Selection 75” kleingrass released by Texas A&M Experiment Station and NRCS in 1968 [3]. Kleingrass is a bunchgrass from South Africa and is adapted to soils ranging from sandy loam to clay [7]. “Midland 99” bermudagrass was released in 1999 by the Oklahoma, Kansas, Arkansas, and Missouri Agricultural Experiment Stations, the Samuel Roberts Noble Foundation, and USDA-ARS [12]. Bermudagrass is well adapted to sandy loam soils and can withstand heavy grazing pressure. “Plains” old world bluestem (Bothriochloa ishaemum) was released in 1972 by the Oklahoma Agricultural Experiment Station and USDA-ARS from lines originating in south-central Asia. It is a bunchgrass with good drought tolerance [13], but it is an aggressive competitor with indigenous grass species [14]. “Pensacola” bahiagrass (Paspalum notatum) was introduced into the US from South America in the late 1930s and is the most widely grown bahiagrass in the US. It can form a dense sod and is often a component of coastal plains pastures. “AU Sand Mountain” bahiagrass is a release from Auburn University from a selection of “Pensacola”. It has been shown to be more winter hardy than other bahiagrass varieties in the Piedmont regions of the southeast [15]. “WW-B. Dahl” (Bothriochloa bladhii) old world bluestem was released in 1994 by USDA-ARS, USDA-SCS, Texas Tech University, and the Texas Agricultural Experiment Station from a selection made in India. It is a bunchgrass with an upright growth habit [16].

2.2. Study Site Description

The study was conducted in 2004 and 2005 at the Noble Foundation’s Pasture Demonstration Farm near Ardmore, OK, USA (34°23′ lat., -97°21′ long.). The soil at the location is a Wilson silt loam (Fine, smectitic, thermic Oxyaquic Vertic Haplustalfs).

Plots were originally established in May, 1998 into a randomized complete block design with three replications and a plot size of 3.0 m × 6.0 m. Incorporated prior to planting, the plot area received 2.24 Mg ha⁻¹ of 100% effective calcium carbonate equivalent lime and 40.0 kg N ha⁻¹ and 103.0 kg P₂O₅ ha⁻¹. From 1999 to 2003, plots were harvested once per year at the end of the growing season. In April, 2004, the plot area was soil-tested to a sampling depth of 152 mm. Based on the results of the soil report, 78.0 kg N ha⁻¹, 52.0 kg P₂O₅ ha⁻¹, and 67.0 kg K₂O ha−1 were applied to the plot area in May. In addition, the plot area was sprayed for broadleaf weeds with 5.0 l ha⁻¹ of 2, 4-dichlorophenoxy acid (2, 4-D). In April of 2005, the plot area was soil-tested to a 152 mm depth. Based on soil test results, 78 kg N ha−1 was applied to the plot area in May. No additional fertilizer amendments were applied. The plot area was sprayed in May, 2005 for broadleaf weeds with 5.0 l ha⁻¹ of 2, 4-D.

2.3. Data Collection

Plots were harvested by species when each species reached the boot stage of reproductive development. This resulted in four harvest dates in 2004 of May 25, June 14, August 03, and September 16. Harvest dates in 2005 were May 23, June 30, August 11, and October 5. Plots were harvested using a Hege plot harvester (Wintersteiger, Inc., Salt Lake City, UT, USA) with a 1.52 m wide sickle-type cutter. A 1.52 m × 6.0 m strip was harvested from the center of each plot, and individual fresh plot weights recorded. A subsample from each plot was collected within each replication. All samples were dried in a forced air oven at 50°C for 3 to 4 days until they reached a constant weight and were then weighed. Dry matter was determined, and yield was reported on a DM basis. The subsamples were then combined within the same species and variety across replications, and one representative sample collected from the combined replications was used for quality determination. Subsamples were ground in a Wiley mill (Thomas Wiley Laboratory Mill, Thomas Scientific, Swedesboro, NJ, USA) to pass a 1 mm screen. Subsamples were analyzed for crude protein (CP) and acid detergent fiber (ADF) using the Foss 6500 NIRS instrument. The samples were scanned using Foss ISIScan software (FOSS NIR Systems, Inc., Laurel, MD, USA). Forage compositional analysis was determined using the Foss Commercial 2001 Grass and Legume Hay prediction equation. The CP mean, standard error of validation, and for the equation used were 17.1%, 0.69%, and 0.98% respectively. The ADF mean, standard error of validation, and for the equation used were 35.1%, 1.3%, and 0.96%, respectively. These equations were then used to predict CP and ADF values for all samples. The total digestible nutrient (TDN) values were calculated using the Penn State equation: NEL = 1.044 − (.0119 * ADF) and TDN = 4.898 + (89.796 * NEL).

2.4. Statistical Analysis

Yield data were analyzed using analysis of variance by the PROC GLM procedure of SAS (SAS Institute Inc., Cary, NC, USA) following a randomized complete block design with replication treated as a random effect. Yield means were separated at . A variety by year interaction for yield was significant (), and therefore results are presented by year. Standard error of the mean was generated for quality using PROC MEANS. All quality concentration data are reported on a dry matter basis.

3. Results and Discussion

3.1. Precipitation

Total precipitation varied little from the long-term average for 2004 and 2005 and was adequate to produce good yields in both years. In 2005, a drier than normal period from March-June followed by above normal precipitation from July-August resulted in an October final harvest for most grasses compared to final harvest in September 2004 (Table 1).

Table 1: Monthly precipitation during the years of 2004 and 2005 and historical long-term average precipitation near Ardmore, OK, USA.

Month
102-year average (mm)a
2004 (mm)
2005 (mm)

January
45.2
30.0
122.0

February
52.3
94.0
50.0

March
74.0
37.0
18.5

April
102.4
108.5
6.6

May
132.3
14.0
90.7

June
101.1
206.0
63.7

July
69.0
140.2
130.3

August
87.1
51.0
159.8

September
91.2
7.9
65.3

October
94.2
169.7
87.9

Total
848.8
858.3
794.5

aOklahoma Mesonet weather data.

3.2. Forage Yield

In 2004, there was no significant difference in total forage yield among “Alamo” switchgrass, johnsongrass, “Selection 75” kleingrass, and “Carostan” flaccidgrass (Table 2) with “Alamo” harvested twice and johnsongrass, kleingrass, and flaccidgrass harvested three times. In 2005, “Alamo” switchgrass produced greater biomass than other grasses in the study over three harvests (Table 3). Johnsongrass, “Selection 75” kleingrass, and “Carostan” flaccidgrass were similar in yield and were harvested three times in 2005 (Table 3). “Alamo” switchgrass exhibited higher yields at the May harvest in both years of the study compared to other grasses (Tables 2 and 3). “Alamo” switchgrass has also been found to be among the highest yielding grasses in other studies in Oklahoma and Kansas [17, 18]. “Alamo” has performed well in both one- and two-cut systems across multiple locations in the Southeast and out yielding upland types as well as the lowland type, “Kanlow” [19]. “Alamo” has also demonstrated long-term yield persistence in an Auburn University planting established in 1988 which has had average yields of 23.1 Mg ha−1 over 13 years [20], but it should be noted that Auburn University is located in a 1321 mm per year rainfall zone. By contrast, “Alamo” switchgrass yields dropped in a two-cut system when harvested in July and again in October [21]. In our study, “Alamo” yields remained consistent with multiple harvests within years and an average of 75 days rest prior to the second cutting. “Midland 99” bermudagrass and “Ermelo” weeping lovegrass produced total yields in excess of 12.6 Mg ha⁻¹ in both years of the study over three harvests.

Table 2: Dry matter yield by harvest month of fifteen warm-season perennial grasses in 2004 near Ardmore, OK, USA.

Species
Yield (kg ha⁻¹)

May
June
Aug.
Sept.
Total

Alamo switchgrass
6129a†
—
10012a
—
16140a

Blue panicgrass
—
—
3415e
1785
5200fg

Blackwell switchgrass
—
9385a
—
—
9385de

Dallisgrass
—
4245bc
3158
—
7403ef

Ermelo weeping lovegrass
3568bc
—
7036
2305
12909bc

Carostan flaccidgrass
4519bc
—
8467
1803
14790ab

Johnsongrass
4712b
—
9260
1665
15637ab

Selection 75 kleingrass
4375bc
—
8829
1982
15186ab

Lometa indiangrass
—
7000ab
—
—
7000ef

Midland 99 bermudagrass
3869bc
—
7323
1809
13000bc

Morpa weeping lovegrass
3276c
—
6281
1988
11545cd

Pensacola bahiagrass
—
3503c
5827
2199
11529cd

Plains bluestem
—
3797bc
—
—
3797g

Sand Mountain bahiagrass
—
—
—
2498
2498g

WW-B. Dahl old world bluestem
—
5192bc
—
—
5192fg

Mean
4350
5520
6961
2004
10081

— indicates that the species was not harvested that month.

†Means within column by the same letter are not significantly different at .

Table 3: Dry matter yield by harvest month of fifteen warm-season perennial grasses in 2005 near Ardmore, OK, USA.

Species
Yield (kg ha⁻¹)

May
June
Aug.
Oct.
Total

Alamo switchgrass
8926a†
—
6757a
3557cd
19240a

Blue panicgrass
996e
1129c
4691b
3023d
9839cde

Blackwell switchgrass
5173bc
—
3908bc
—
9081de

Dallisgrass
—
4685a
—
5020bc
9705cde

Ermelo weeping lovegrass
5444b
—
4039bc
3195d
12678bcde

Carostan flaccidgrass
4986bc
—
4834ab
2212d
12032bcde

Johnsongrass
4855bc
—
3195bc
2462d
10512bcde

Selection 75 kleingrass
6030b
—
5189ab
2751d
13970b

Lometa indiangrass
—
5392a
—
5677ab
11069bcde

Midland 99 bermudagrass
5970b
—
4445b
2951d
13366bc

Morpa weeping lovegrass
4201cd
—
3862bc
2854d
10917bcde

Pensacola bahiagrass
3182d
1514bc
3640bc
2778d
11114bcde

Plains bluestem
—
4311ab
—
3141d
7452e

Sand Mountain bahiagrass
2785d
—
2221c
2561d
7567e

WW-B. Dahl old world bluestem
—
4688a
—
7063a
11751bcd

Mean
4777
3620
4253
3518
11353

— indicates that the species was not harvested that month.

†Means within column followed by the same letter are not significantly different at .

3.3. Forage Quality

Large quality differences were not apparent for grasses evaluated in the study (Tables 4 and 5). The exceptions were “Pensacola” bahiagrass and “WW-B. Dahl” old world bluestem which exhibited CP levels below 50 g kg⁻¹ in the final harvest of 2005. In 2004, their quality had been similar to other grasses in the study. Mean CP declined 46% from May to August in both years of the study. In the May harvest of 2004, CP of all grasses harvested was above 108 g kg⁻¹ except, “Midland 99” bermudagrass which was 86.0 g kg⁻¹ (Table 4). CP at or above 108 g kg⁻¹ would be a sufficient protein level to support a 272.4 kg stocker daily gain of  .681 kg; however, TDN percent in the grasses was limiting and would need supplementation [22]. In May 2005, CP of the grasses is expected to support good stocker daily gains with the exception of “Alamo” switchgrass and “johnsongrass” which had CP levels slightly below 108 g kg⁻¹ (Table 5). TDN of the grasses is limiting with expected stocker daily gains based on nutrient analysis of  .454–.681 kg/day. The exception was “Midland 99” bermudagrass which could support a 272.4 kg stocker daily gain of  .681 kg [22]. The forage quality of grasses measured in May meets the nutritional requirements of mature beef cows for the first 90 days after calving. Even though forage quality begins to decline from May to June, the forage quality of these grasses would still meet nutritional requirements of gestating cows’ from the middle to last 1/3 of pregnancy. In later months of the grazing season supplementation would be required to meet beef cow nutritional demand [22].

Table 4: Dry matter crude protein (CP), total digestible nutrient (TDN), and acid detergent fiber (ADF) by harvest month of fifteen warm-season perennial grasses in 2004 near Ardmore, OK, USA.

Species
(g kg⁻¹)

May
June
August
September

CP
TDN
ADF
CP
TDN
ADF
CP
TDN
ADF
CP
TDN
ADF

Alamo switchgrass
115
590
393
—
—
—
43
496
477
—
—
—

Blue panicgrass
—
—
—
—
—
—
68
512
463
162
646
343

Blackwell switchgrass
—
—
—
79
514
461
—
—
—
—
—
—

Dallisgrass
—
—
—
97
532
445
80
549
430
—
—
—

Ermelo weeping lovegrass
113
574
407
—
—
—
57
539
439
70
569
412

Carostanflaccidgrass
116
580
402
—
—
—
42
471
500
96
549
430

Johnsongrass
108
576
406
—
—
—
40
479
493
101
590
393

Selection 75 kleingrass
123
613
372
—
—
—
64
561
419
103
635
353

Lometaindiangrass
—
—
—
66
530
447
—
—
—
—
—
—

Midland 99 bermudagrass
86
599
385
—
—
—
51
584
398
88
589
394

Morpa weeping lovegrass
108
564
416
—
—
—
59
548
431
76
578
404

Pensacola bahiagrass
—
—
—
104
578
404
84
572
409
86
569
412

Plains bluestem
—
—
—
96
512
463
—
—
—
—
—
—

Sand Mountain bahiagrass
—
—
—
—
—
—
—
—
—
121
619
367

WW.B-Dahl old world bluestem
—
—
—
84
555
442
—
—
—
—
—
—

Mean
110
585
397
88
537
441
59
531
446
100
594
390

Standard error†
4.4
6.3
5.7
5.7
10.3
9.3
4.9
12.4
11.2
9.2
11
9.8

— indicates that the species was not harvested that month.

†Standard errors are calculated within columns.

Table 5: Dry matter crude protein (CP), total digestible nutrient (TDN), and acid detergent fiber (ADF) by harvest month of fifteen warm-season perennial grasses in 2005 near Ardmore, OK, USA.

Species
(g kg⁻¹)

May
June
August
October

CP
TDN
ADF
CP
TDN
ADF
CP
TDN
ADF
CP
TDN
ADF

Alamo switchgrass
97
567
414
—
—
—
69
563
419
82
581
395

Blue panicgrass
171
602
369
194
650
307
91
569
411
52
536
453

Blackwell switchgrass
127
599
370
—
—
—
75
569
411
—
—
—

Dallisgrass
—
—
—
153
606
360
—
—
—
56
516
479

Ermelo weeping lovegrass
110
578
399
—
—
—
76
536
453
63
531
460

Carostanflaccidgrass
159
599
372
—
—
—
67
551
435
65
544
443

Johnsongrass
101
561
421
—
—
—
71
558
425
69
549
436

Selection 75 kleingrass
121
581
396
—
—
—
60
546
440
59
560
423

Lometaindiangrass
—
—
—
112
581
396
—
—
—
55
525
467

Midland 99 bermudagrass
179
645
314
—
—
—
64
579
398
81
593
380

Morpa weeping lovegrass
127
592
381
—
—
—
68
543
444
61
530
462

Pensacola bahiagrass
133
582
395
133
586
389
76
565
417
65
548
438

Plains bluestem
—
—
—
107
551
434
—
—
—
24
481
524

Sand Mountain bahiagrass
153
619
347
—
—
—
78
573
405
74
557
426

WW-B. Dahl old world bluestem
—
—
—
121
608
361
—
—
—
34
520
474

Mean
134
593
380
137
597
375
72
559
423
60
541
447

Standard error†
8.4
7.2
9.2
13.2
13.5
17.4
2.5
4.1
5.3
4.3
7.5
9.6

— indicates that the species was not harvested that month.

†Standard errors are calculated within columns.

3.4. Forage Yield Distribution

Figure 1 is the average two-year forage distribution based on total average yield of the fifteen warm-season perennial grasses in this study over harvest dates. Greater total yield potential exists with the grasses that have at least 1/3 of their total forage production occurring early in their growing season. These include “Alamo” switchgrass, “Selection 75” kleingrass, “Midland 99” bermudagrass, johnsongrass, “Carostan” flaccidgrass, and “Ermelo” weeping lovegrass. This early season production also offers forage quality sufficient for postpartum mature cows or, with some supplementation, stocker production. After May harvests, these grasses accumulated yields by the August harvest that surpassed May production demonstrating their potential for substantial biomass accumulation by the end of the growing season. Yield distribution of “Alamo” switchgrass is similar to what has been reported in Tennessee [23]. This ability to produce good yields after May would then suggest that these grasses could be used as dual-purpose grasses for both livestock production and cellulosic ethanol production. Other grasses in the study do not display the yield potential or the seasonal distribution to be used as dual-purpose forages.

Figure 1: Average monthly percent yield distribution of the total dry matter yield produced from May through October among fifteen warm-season perennial grasses near Ardmore, OK, USA.

4. Conclusions

“Carostan” flaccidgrass, johnsongrass, and “Selection 75” kleingrass produced similar yields to “Alamo” switchgrass in 2004 but, “Alamo” switchgrass was the highest producing entry in 2005 and would still be considered the standard for biomass production in the region. However, many producers in the southern Great Plains are currently growing bermudagrass, weeping lovegrass, kleingrass, and johnsongrass and are familiar with their establishment and production characteristics. Producers may be willing to produce biomass for biofuel if their existing forage base can be utilized for early season grazing and hay production followed by deferment for biomass accumulation. Because of the early season production potential and quality of “Carostan” flaccidgrass, johnsongrass, “Midland 99” bermudagrass, “Ermelo” weeping lovegrass “Selection 75” kleingrass, and “Alamo” switchgrass, they could be used as a source of both cellulosic biofuel and forage. Seed sources of flaccidgrass are limited, however flaccidgrass can be sprigged but research into sprigged production and establishment needs to be undertaken. The remaining grasses in the study were slower to initiate spring growth, and the regrowth potential following harvest compared to the top grasses in the study was low which lowered their total yearly production.

As the cellulosic biofuels industry continues to develop, the enzymatic processes used for cellulose extraction will improve thereby expanding potential sources of cellulosic biomass. Based on the results of this study in addition to “Alamo” switchgrass; “Selection 75” kleingrass, “Midland 99” bermudagrass, “Ermelo” weeping lovegrass, “Common” johnsongrass, and “Carostan” flaccidgrass have potential as dual-purpose grasses for forage and biofuel.

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