Getting your N application correct can boost switchgrass production

Doo-Hong Min, Michigan State University Extension - May 31, 2012

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	1.6^a	2.9^a	2.2^a
150	2.1^b	3.5^ab	2.9^b
100	2.3^b	4.2^b	3.4^b
150	2.5^b	5.6^c	3.6^bc
200	2.4^b	5.2^c	3.1^bc
50	2.7^b	5.1^c	3.0^c
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	7,290^a	42^a
50	7,140^a	51^ab
100	7,110^a	59^b
150	7,140^a	80^c
200	7,230^a	75^c
250	7,300^a	75^c
Mean	7,200	64

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

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).