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.
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