Getting your N application correct can boost switchgrass production

Switchgrass has caught the attention of farmers as a potential bioenergy crop due to rising oil prices.

Nitrogen input is an important aspect of growing switchgrass and three years ago nitrogen fertility on switchgrass was conducted in Michigan’s Upper Peninsula. The objective of this study was to determine the optimum application rate of nitrogen fertilizer for switchgrass as a bioenergy crop. There were six nitrogen application rates (0, 50, 100, 150, 200, and 250 pounds N/acre) with four replications and “Cave-in Rock” variety was used in this study.

Based on three-year data from 2007-2009, 150 pounds of N per acre appears to be the optimum rate to grow switchgrass. The three-year average dry matter yield at the 150 pounds N treatment was 3.9 dry matter tons/acre/year. There was no further yield increase beyond 150 pounds of N per acre (Table 1). There was no difference in heating value—measured in British thermal units (BTU)—per pound of dry matter in different nitrogen application rates and the average heating value over nitrogen application rates were 7,200 BTU per pound of dry matter (Table 2). Like the trend in dry matter yield, there was no further increase in heating value per acre beyond 150 pounds of N per acre. The data indicates that switchgrass can be grown at a rate of 150 pounds of N per acre in the Michigan’s Upper Peninsula with a good heating value.

Table 1. Switchgrass Nitrogen Fertility Trial Yield (DM Ton/A) in Chatham

Rate (pounds N/A)

2007

2008

2009

0

1.6a

2.9a

2.2a

150

2.1b

3.5ab

2.9b

100

2.3b

4.2b

3.4b

150

2.5b

5.6c

3.6bc

200

2.4b

5.2c

3.1bc

50

2.7b

5.1c

3.0c

Mean

2.3

4.4

3.0

*Means of the same column with different superscripts significantly differ (p<0.05).

Table 2. Heating Values of Switchgrass Nitrogen Fertility Trial (2008) in Chatham

Rate (pounds N/A)

BTU/DM pounds

Million BTU/acre

0

7,290a

42a 

50

7,140 a

51ab

100

7,110 a

59b

150

7,140 a

80c

200

7,230 a

75c

250

7,300 a

75c

Mean

7,200

64

*Means of the same column with different superscripts significantly differ (p<0.05).

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