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Switchgrass Biomass Production in the Midwest USA

Harvest and Nitrogen Management

^a USDA-ARS, 344 Keim Hall, Univ. of Nebraska, Lincoln, NE, 68583
^b Dep. of Agron., 279 Plant Sciences, Univ. of Nebraska, Lincoln, NE 68583
^c USDA-ARS, 5601 Sunnyside Ave., Beltsville, MD 20705-5139

View larger version (37K): [in a new window]   Fig. 1. Biomass yields of first harvest or cut and regrowth harvest for eight harvest treatments at Ames, IA, and Mead, NE, averaged over 1994 and 1995 and over N rates. Harvest treatments are two- or one-cut harvests based on initial harvest dates starting in late June or early July (Harvest 1) and continuing at approximately weekly intervals until the latter part of August (Harvest 7). A final eighth harvest was completed after a killing frost, at which time regrowth was also harvested on previously harvested plots for Harvest Treatments 1 through 7.

View larger version (14K): [in a new window]   Fig. 2. Biomass yields of first harvest or cut and regrowth harvest with increasing rates of N at Ames, IA, and Mead, NE, averaged over harvest treatments for 1994 and 1995. Regression equations were Ames cut 1, Y = 6.9 + 0.036X - 0.00007X2, r2 = 0.98, root mean square error (RMSE) = 0.3; Ames cut 2, Y = 1.29 + 0.0039X, r2 = 0.90, RMSE = 0.2; and Mead cut 1, Y = 8.38 + 0.0055X, r2 = 0.70, RMSE = 0.5.

View larger version (40K): [in a new window]   Fig. 3. Nitrogen removal in first and regrowth biomass harvest or cuts for switchgrass biomass harvest treatments at Ames, IA, and Mead, NE, averaged across N treatments for 1994 and 1995.

View larger version (18K): [in a new window]   Fig. 4. Biomass N concentration of first harvest and regrowth harvest or cut with increasing rate of N fertilization at Ames, IA, and Mead, NE, in 1994 and 1995. Regression equations were Ames cut 1, Y = 9.6 + 0.023X - 0.000019X2, r2 = 0.99, RMSE = 0.2; Ames cut 2, Y = 12.1 + 0.006X, r2 = 0.91, RMSE = 0.2; Mead cut 1, Y = 7 + 0.04X, r2 = 0.99, RMSE = 0.2; and Mead cut 2, Y = 9.1 + 0.013X, r2 = 0.96, RMSE = 0.3.

View larger version (18K): [in a new window]   Fig. 5. Nitrogen removal in first and regrowth biomass harvests or cuts from switchgrass plots treated with increasing rates of N rates at Ames, IA, and Mead, NE, averaged over 1994 and 1995. Regression equations were Ames cut 1, Y = 43 + 0.58X - 0.00008X2, r2 = 0.99, root mean square error (RMSE) = 1.2; Ames cut 2, Y = 9.5 + 0.063X, r2 = 0.98, RMSE = 1.1; Mead cut 1, Y = 80 +0.19X, r2 = 0.96, RMSE = 4.8; and Mead cut 2, Y = 15 + 0.02X, r2 = 0.98, RMSE = 0.3.

View larger version (20K): [in a new window]   Fig. 6. Response of 1996 switchgrass biomass yields harvested in August to spring 1996 soil NO3–N concentrations for plots on which harvest and N rate treatments were applied in 1994 and 1995 at Ames, IA, and Mead, NE. Regressions were not significant for either location, with r2 values of 0.02 and 0.14 for Ames and Mead, respectively.