Kenneth Vogel, Research Geneticist
Marty Schmer, Research Technologist
Rob Mitchell, Rangeland Scientist, USDA-ARS, Lincoln, NE
Richard Perrin, Professor, Agricultural Economics, University of Nebraska-Lincoln
Materials and Methods
Results and Discussion
• South Dakota
• North Dakota
• Northern Great Plains
Switchgrass, a native prairie grass, has been identified as a potential biomass energy crop. Although switchgrass has been used as a pasture grass and for conservation purposes, it has not been grown and managed as a commercial biomass energy crop. Biomass yields and productions costs associated with production of energy from switchgrass have been estimated from small plot and laboratory data. To obtain field-scale biomass yields and production costs, we contracted with eleven producers in the Northern Plains states of Nebraska, South Dakota, and North Dakota to grow and manage switchgrass as a biomass energy crop. The cooperators' fields range in size from 15 to 23 acres, and are located from southern Nebraska to northern North Dakota. Harvested area of one field has been reduced in size to 7 acres. The fields selected had characteristics that would have qualified them for the Conservation Reserve Program (CRP) and are typical of the surrounding geographical region. The land base for herbaceous energy crops will likely be CRP-type land. The Nebraska fields were planted in 2000 and the South and North Dakota fields were planted in 2001. In this report, we summarize biomass yields and stands by individual farms for the four or five year period.
Materials and Methods
The fields were planted with adapted switchgrass cultivars in May or early June. The cultivars varied with the latitude of the farms. The cultivars Trailblazer, Shawnee, or Cave-in-Rock were used in Nebraska. All fields in South Dakota were planted to Trailblazer except for the field at Ethan which was planted to Shawnee. In North Dakota, Sunburst was used on all fields. Herbicides were used for weed control and varied with state. Best weed control was obtained using a pre-emergence mixture of atrazine and quinclorac (Paramount®). Each year, stand frequencies have been obtained using a simple frequency grid. A frequency grid can be made from concrete reinforcing mesh and is simply a 30 x 30 inch metal frame that is subdivided in 25 cells that measure 6 x 6 inches. After emergence the establishment year or after spring green-up the post-establishment years, the grid is placed on the ground at a site within a field and the number of cells that contain a switchgrass plant are counted. The grid is flipped end-to-end and counts are taken three more times until a total of 100 cells are counted. The number of cells that contain a switchgrass plant is the stand frequency. We repeated the process over ten times within each field to obtain a field average. It typically takes less than an hour to measure stands on a field. Based on previous research and this study, stand frequencies of 40% or greater for switchgrass can be classified as good to excellent. Fields with stand frequencies of 25 to 40% can develop into good stands with proper management without reseeding. Stands with frequencies less than 25% need additional inputs including re-seeding.
No fertilizer was applied the establishment year. In the post-establishment years, nitrogen fertilizer has been applied in the spring at rates which ranged from 60 to 100 lb N/acre. Nitrogen fertilizer rate varied due to precipitation and the yield potential of the field. To obtain optimal use of N fertilizer, recently completed research indicates that 20 lbs of N need to be applied for each ton of potential yield.
In the establishment year, the fields were rated as harvestable if estimated yields exceeded 0.5 tons per acre. In the establishment year, harvests should be delayed until after a killing frost. If a field was not harvested the establishment year, it was mowed or burned the following spring prior to spring green-up. In the post-establishment years, switchgrass biomass was harvested either after the fields were fully headed in late July or early August or after a killing frost in the fall. Cutting height was four inches. Yields have been determined by clipping and weighing a minimum of ten 12 sq. ft areas (quadrants) within a field and by counting and weighing bales. The quadrant harvests were taken to obtain estimates of yield variation across fields and are good estimators of total biomass yield.
Results and Discussion
Abnormally dry conditions existed in central and eastern Nebraska in 2000. Moisture conditions were near normal for most parts of Nebraska, South Dakota, and North Dakota in 2001. In 2002, abnormally dry conditions existed throughout most of Nebraska, central South Dakota, and southern North Dakota. Moisture conditions were variable across the region in 2003 and in 2004, precipitation was approximately average for the region.
Two Nebraska farms were located in the southern part of the state (Douglas and Lawrence) and two were located in northern Nebraska (Crofton and Atkinson). Adequate stands were obtained at all fields except for the field at Atkinson, Nebraska which had to be replanted due to drought (Figure 1). The soil at this site is very sandy. Stands have steadily improved over time and in 2004, all fields had excellent stand frequencies of about 80%. The fields at Douglas and Lawrence produced harvestable yields the establishment year. Grassy weeds limited switchgrass yields at Crofton the establishment year. In the post establishment years of 2001 and 2002 which were dry years, biomass yields ranged from 0.5 to 3 ton/acre. In 2003 and 2004, yields ranged from 3 to 4 tons per acre on the Nebraska fields.
Very good stands were obtained on all the South Dakota fields in 2001 except for the field at Ethan where no herbicides were applied (Figure 2). In the year after establishment, a herbicide application of atrazine and quinclorac enabled an adequate stand to develop at this site. Pre-emergence application of quinclorac was used on the fields at Huron and Bristol. Additional herbicides were used at Bristol to address specific weed problems. At Highmore, glyphosate was applied pre-emergence and atrazine and quinclorac were applied the spring after establishment. Stands on all fields have increased over time and have stabilized at stand frequencies of 60% to 80%. Harvestable yields were obtained the establishment year on both the Huron and Bristol fields.
The biomass at Ethan in Year 1 (2001) consisted mostly of weeds and was not harvested. Due to drought, the field at Highmore did not produce harvestable yields in either 2001 or 2002 (Year 1 and 2). In 2003 and 2004 which have been more “normal” in precipitation, switchgrass biomass yields on the South Dakota fields have ranged from about 3 to 5 tons/acre.
Initial stands were low on the fields at Streeter and Munich, North Dakota (Figure 3). The field at Streeter was seeded into a field that was converted from oats and the herbicides that were used did not adequately control the oats. With good management including the use of herbicides to control specific weeds, the stands have improved. The field at Munich was planted using a grain air seeder followed by light tillage. Stands were erratic across the field even though pre-emergence herbicides were used. The stands have been improved by delaying biomass harvest until after a killing frost allowing seeds to shatter.
Biomass yields in 2003 and 2004 ranged from 2 to over 4 tons per acre at the two fields. Another field was planted near Underwood, North Dakota but inadequate stands have been obtained even though the field was entirely replanted. We believe the problem has been high soil pH. Recently completed research at the USDA-ARS Northern Great Plains Research Laboratory has shown that switchgrass germination is significantly reduced at pH levels of 8 or higher.
Northern Great Plains
In the Northern Great Plains states, switchgrass biomass yields of over 3 tons per acre can be produced on CRP-type fields on farms in this region using existing cultivars and production technology (Figure 4). Existing cultivars were developed for use in pastures and not for biomass energy. It should be feasible to increase biomass yields using cultivars bred for use as biomass energy crops and improved management practices. The results of these field studies clearly demonstrate the need to obtain good stands and harvestable yields the establishment year. This requires high quality seed, good seedbed preparation, and establishment year weed control with herbicides.
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