Evaluation of Herbaceous Biomass Crops in the Northern Great Plains: Introduction and Objectives

Herbaceous lignocellulosic crops are a potential renewable feedstock for biochemical or thermochemical conversion systems second in size only to wood products. If the long-term goal of the Department of Energy is to produce significant quantities of energy from renewable sources that is cost effective with other fuels, it is important that several herbaceous biomass crops and their management be evaluated in various regions of the United States.

Little information was available on the productive potential of herbaceous crops used for biomass production in the northern Great Plains prior to initiation of this project. What information available was obtained in evaluation of forage crops for livestock feed, but these data do not apply well to biomass production because forage quality, and not quantity, determines management practices.

Meyer (1979) evaluated sweet sorghum (Sorghum bicolor (L.) Moench) for its adaptation to the northern Great Plains. Maximum biomass yields of 17 genotypes evaluated was less than 15 Mg ha-1 under irrigated conditions in an average year, but sugar accumulation in the stalks was very low compared with other regions. He concluded from this 1-year experiment that the environment at Fargo, ND, was too cool for consistent production.

Even less information was available on biomass production on marginal or idle (summer fallowed) cropland. The conservation reserve program (CRP) idled in excess of 1.3 million hectares in North Dakota alone. These CRP hectares represent a major land resource available for biomass production with herbaceous crops.

Idled cropland or fallow hectarage is the second block of land potentially utilizable for energy crop production. North Dakota alone has nearly 2.9 million hectares fallowed annually. Badaruddin and Meyer (1989) and Meyer (1987) have previously shown that a legume forage crop could be harvested in eastern North Dakota without substantially affecting subsequent crop productivity in average to above-average precipitation years. But, we need to determine the extent of fallow hectarage that could be tapped for leguminous biomass production and/or the effect of biomass cropping on subsequent crop productivity from not having fallow available for next year's crop production.

To be a viable alternative cropping enterprise, biomass cropping must compete economically with other cropping alternatives in the area. Land costs are relatively cheap and returns from competing cropping alternatives are relatively low in the northern Great Plains compared with other areas of the United States. Therefore, even though biomass yields may be lower than that produced in other areas, cost per unit of biomass may be cheaper.

The primary goal of this project was to evaluate the potential of several herbaceous biomass crops in the northern Great Plains. Our specific 5-year objectives included:

1. Determine the biomass yield and select chemical composition of four annuals and at least six perennial herbaceous lignocellulosic crops at three good cropland sites, two marginal cropland sites, and one irrigated site in North Dakota.
2. Determine the effect of management intensities [nitrogen (N) level for all species and crop- fallow for annual crops] on biomass yield and chemical composition of four annual and at least six perennial crops across a precipitation gradient.
3. Determine the potential biomass yields on normal fallowed land and its effect on subsequent crop yields.
4. Evaluate the economic feasibility of the various herbaceous energy crops compared with competing crops in the northern Great Plains.

Objectives 1 and 2

Detailed description of materials and methods used in this series of field experiments conducted to meet the objectives are presented elsewhere by Meyer et al. (1989-93). A brief overview of the project follows.

Field experiments were conducted at six North Dakota sites during 1988 to 1992. Five dryland sites and one irrigated site representative of the three major soil areas or regions of North Dakota were chosen (Figure 1). Site 1 is located in the Red River Valley of the North at Prosper, ND, on a productive Gardena silt loam soil (coarse-silty, mixed, Pachic Udic Haploboroll) about 40 km northwest of Fargo, ND. Site 2 is located on the Hettinger Research and Extension Center at Hettinger, ND, on a productive Shambo silt loam soil (fine-loamy, mixed, Typic Haploboroll), and is representative of farmland south and west of the Missouri River in an unglaciated region of the Missouri Plateau. Site 3 (Glenfield Good) is located near Glenfield, ND, on a productive Barnes loam gradating to a Svea loam soils (fine-loamy, mixed, Udic Haploborolls) with numerous rocks typical of the Drift Prairie of east-central North Dakota.

Sites 4 and 5 are marginal cropland locations that qualify as CRP hectarage. Site 4 is located at Leonard, ND, on a fairly productive, Hecla loamy fine sand (sandy, mixed, Aquic Haploboroll), which is highly susceptible to wind erosion. This site is located about 48 km southwest of Fargo (Figure 1). Site 5 (Glenfield Poor) is located near Glenfield, ND, on the crest of hills, which is typical of the poor soil types in the Drift Prairie. The soil is a Buse loam (fine-loamy, mixed, Udorthenthic Haploboroll). Site 6 (Carrington irrigated) is located at the Carrington Research and Extension Center at Carrington, ND, and is an irrigated site in the Drift Prairie. Detailed description and the physical and chemical makeup of the soils at each site were presented by Meyer et al. (1991). Soil loss estimated by the universal soil-loss equation for each site was reported by Meyer et al. (1992).

These six sites normally have a precipitation gradient with Carrington the greatest (irrigated), Prosper and Leonard intermediate, Glenfield next, and Hettinger least. Normal precipitation for the growing season at each site is presented in Table 1.

Ten perennial species/mixtures were evaluated including four cool-season grasses ('Palaton' reed canarygrass, Phalaris arundinacea L.; common bromegrass, Bromus inermis Leyss.; 'Nordan' crested wheatgrass, Agropyron desertorum (Fisch. ex Link) Schult.; and 'Ohae' intermediate wheatgrass, Thinopyrum intermedium (Host) Barkw. & D.R. Dewey), two warm-season grasses ('Sunburst' switchgrass, Panicum virgatum L. and SD 43 big bluestem, Andropogon gerardii Vitman var. gerardii), and four mixtures (brome- alfalfa, Medicago sativa L.; intermediate-western wheatgrasses, Pascopyrum smithii (Rydb.) A. Löve; switchgrass-brome; and a CRP mixture [intermediate wheatgrass, tall wheatgrass (Thinopyrum ponticum (Podp.) Barkw. & D.R. Dewey), alfalfa, and sweetclover (Melilotus officinalis Lam.)]. The last mixture was chosen since this "wildlife mixture" is a common mixture used on CRP hectarage.

All cool-season perennial plots were seeded at 323 seeds m^-2, except reed canarygrass which was doubled, following careful seedbed preparation during the last week of April and first week of May 1988. Warm- season species were seeded the third week of May, typical recommended dates for these species. A specially design drill by researchers at the Northern Great Plains Research Center at Mandan, ND, was used to seed all plots. Unique characteristics of this seeder includes a series of packer wheels replacing the normal drive wheels of the power unit, which firms the seedbed and permits precise, shallow seeding; depth bands set at 2-cm seeding depth on the double-disc openers; cone seeder with rotating spreader; and rear packer wheels. This drill normally gives excellent stands of small-seeded species/mixtures in the semi-arid environment of the northern Great Plains. The seeder plants 10 rows on 15-cm centers. An experimental unit was 7.6 m in length by 1.5 m in width.

All perennials were seeded during late April and early May, but marginal stands occurred at all sites due to the near record drought of 1988; therefore, cool-season species/mixtures at all sites were reseeded or renovated (Glenfield Poor) during 15 to 22 August using similar techniques to the spring seedings. Warm-season species were seeded the following spring. The new seedings at Prosper, Leonard, and two Glenfield sites were watered (approximately 0.8 cm per application) once or twice a week starting 1 week after planting until the first week of October to aid germination and establishment. The sites were watered as frequently as possible with a 1512-L tank on the back of a pickup truck. Fortunately, adequate rainfall and cooler temperatures in September allowed establishment of good stands at these sites.

The number of plants m-2 and average growth stage were determined for each of the seven species/mixtures in two replicates at Prosper and Leonard sites in October 1988. In general, the majority of species/mixtures had stand densities of 215 to 323 plants m-2 and was in the 2 to 4-leaf stage. Meyer and Rugroden (1988) reported that as little as 11 uniformly distributed plants m-2 produced fully productive stands by the second harvest year. Observations at Glenfield and Carrington indicated similar progress, but plants were in the 1 to 2-leaf stage. Plants at the Hettinger site did not emerge due to lack of precipitation.

Stand evaluations in spring 1989 indicated good to excellent grass stands at Carrington, Prosper, Leonard, and Glenfield Good and Poor sites, but the legume component was very poor. Therefore, a broadcast seeding of the legumes was performed at each site but with little success. Warm-season species were reseeded at all sites and the cool-season species/mixtures at Hettinger in 1989. Unfortunately, warm-season grass establishment was poor at most sites except Prosper and, to a lesser degree, Leonard. Cool-season species/mixtures at Hettinger established only marginal stands.

All established perennial cool-season species/mixtures were fertilized with N (urea, 46-0-0) at 0, 50, and 100 kg ha^-1 beginning spring 1989. An additional N level of 200 kg ha-1 was used at Carrington and Prosper. Subsequent year's fertilization occurred in late October. All warm-season perennial plots considered established were fertilized with N at the same rates in mid May to help reduce cool-season grass encroachment.

The field design for the perennial experiments was a randomized complete block in a split-plot arrangement. The mainplots were species and the subplots were N levels. Three replicates were used at all sites.

Cool-season grasses/mixtures were harvested with a flail mower in July each year and warm-season grasses in August. The harvested area was 0.86 by 6.12 m or 5.26 m². Biomass of each plot was weighed to determine field weight, sampled for moisture, and the sample dried in a force-air oven at 50oC. The samples were ground to pass a 1-mm screen in a Wiley mill, mixed thoroughly, subsampled, and stored in sealed plastic or glass containers until chemical analyses were performed. All remaining biomass in the field after harvest was removed. Regrowth usually was minimal and left standing in the field. A second harvest was taken at Leonard in 1990.

Annual herbaceous species used at the six sites were 'Pioneer 3974' corn , Zea mays L., for grain; DeKalb variety FS25E forage sorghum, Sorghum bicolor (L.) Moench; DeKalb variety ST6E sorghum X sudangrass cross (sorghum X sudan); 'German' foxtail millet, Setaria italica (L.) P. Beauv.; common sweetclover, and common kochia, Kochia scoparia L. Sweetclover and kochia were planned to be volunteering species. Corn was included as an environmental check and was over seeded and thinned to 69,000 plants ha^-1 at Carrington and 44,500 plants ha^-1 at other sites. The sorghums were seeded at 28 kg ha^-1, foxtail millet at 22 kg ha^-1, sweetclover at 10 kg ha^-1, and kochia at about 5 kg ha^-1. An experimental unit consisted of four rows spaced 61 cm apart for corn and sorghums, eight 30-cm rows for foxtail millet, and broadcast stands for kochia. All plots were 6.12 m in length.

Management intensities included were crop-recrop initiated in 1989 and N levels. Hard red spring wheat (Triticum aestivum L. emend. Thell.) usually was the recrop species. The sorghums and foxtail millet were fertilized with urea at 50, 100, and 200 kg N ha^-1. It became apparent in 1989 that the volunteering kochia and sweetclover treatments would not work so they were discontinued and only an annually seeded kochia treatment fertilized at 50 kg N ha^-1 was included instead. Kochia and sweetclover were unfertilized in 1988.

The field design for annual experiments was a randomized complete block with a split-split-plot arrangement. Crop-recrop was the mainplot, species the subplot, and N level the sub-subplot. A split-plot analysis was used when the crop-recrop comparison was not included.

The annuals were seeded in well-prepared seedbeds usually during mid May. Nitrogen fertility treatments were applied immediately following planting. Weed control was via herbicides and hand-weeding where deemed necessary. Corn and sorghum treatments at all sites were sprayed postemergence with atrazine, 6- chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine, at 1.12 kg ha^-1 and crop oil (3.78 L ha^-1. Foxtail millet plots were wheel-hoed twice since millet is injured easily by atrazine. Kochia treatments had no weed control practices applied.

Biomass yields of row-crop annuals were determined by hand harvesting during September. Foxtail millet and kochia were harvested with a Jari mower about 2 weeks before a killing frost to prevent seed drop. A middle row of corn and sorghum, two middle rows of foxtail millet, and an area of kochia 86-cm wide by 4.5 m in length constituted the harvest plot. All samples from each treatment were handled similar to perennial samples.

Select chemical composition was determined on all samples from two replicates of all perennial and annual biomass species and for all management-intensity treatments. Acid-detergent fiber (ADF), neutral- detergent fiber (NDF), and acid-detergent lignin (ADL) concentrations were determined by the methods of Goering and Van Soest (1970). Hemicellulose was calculated as NDF-ADF and cellulose as ADF-ADL. Nitrogen, ash, and dry matter concentrations were determined by AOAC methods. Total nonstructural carbohydrate (TNC) concentration was determined using procedures of Smith (1980). Biomass yields are reported on the dry matter basis. Yields of chemical components were determined by multiplying the biomass yield by the appropriate chemical constituent. Average concentration of the two replicates determined was used to calculate yields in the third replicate.

Analyses of variance using the SAS system were determined on biomass yields, chemical component concentrations, and chemical component yields. Appropriate analyses for a randomized complete-block design with treatments in a split (perennials) or split-split-plot (annuals) arrangements were used. Species, N levels, and cropping treatments were considered fixed effects. Years and sites were considered random effects. Where significant F-tests were detected, least significant differences (LSD) were used to separate means. Two separate analyses were determined on the annuals due to the unbalanced nature of the treatments. First, species significance was determined by deleting all fertility treatments above 50 kg N ha-1 from the data set. Second, kochia treatments were deleted, and the cropping system, fertility level, and two- and three-way interactions determined. Reported significance for these effects was based on these analyses.

Biomass cropping across a precipitation gradient was evaluated by plotting biomass yields (meaned across N levels) for each perennial and recrop annual species at each site and year versus growing-season precipitation. Linear regression equations were calculated and goodness of fit evaluated by the coefficient of determination (r2).

Objective 3

'Nitro' alfalfa and common sweetclover were seeded without a companion crop on recrop land at Carrington, ND, in 1990. Trifluralin, 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine, at 0.7 kg ha^-1 was preplant incorporated for weed control. In addition, a 'Stoa' spring wheat treatment fertilized with 100 kg N ha^-1 and a fallow treatment were included as common farming practices of the area. Plots were arranged in the field in a randomized complete-block design, and three replicates were used. Similar experiments were seeded in 1988 and 1989, but inadequate stands occurred due to the extreme droughty conditions (Table 1) and the experiments abandoned.

Biomass harvests were taken 15 Aug. 1990 on 1-cut alfalfa and sweetclover plots and again 12 October on 2-cut alfalfa plots by harvesting an area of at least 7 m². Samples for dry matter determination were dried at 50oC. Following the second harvest, half the plots were rototilled to incorporate all remaining vegetation while the remaining plots left the vegetation stand over the winter attempting to trap snow to replace some of the soil moisture utilized by the biomass crop.

In 1991, Stoa wheat and 'Hazen' barley (Hordeum vulgare L.) were seeded at 80 and 60 kg ha^-1, respectively, across all 1990 treatments following a field cultivator seedbed preparation. The field design was a randomized complete block with treatments in a split-plot arrangement. Cropping treatment in 1990 was the mainplots, wheat or barley the subplot, and N level the sub-subplot. Nitrogen at 0, 75, and 150 kg ha^-1 was applied as urea immediately following seeding. Weeds were controlled with a 1.12 kg ha^-1 application of diclofop, (±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid, and 2,4-D. Grain was harvested in early August with a Hege combine. Harvest plot was 1.2 by 6 m. All wheat and barley grain samples were cleaned, dried, and grain yield expressed on 140 or 120 g kg^-1 moisture concentration, respectively.