In June 2010 we published an Ag News & Views article entitled Nutrient Requirements for Switchgrass Production. Expanding on that theme, let's examine switchgrass forage yields and quality over a growing season when the crop is properly managed. In 2008 and 2009, we recorded production and quality data from Alamo switchgrass grown on a slaughterville fine sandy loam soil near Burneyville, Okla. According to soil tests, all nutrients were adequate except nitrogen (N), so we applied 70 pounds actual N per acre in early April. Forage production was measured biweekly beginning in April when switchgrass reached 14 inches in height until the end of July. Measurements were also taken at plant maturity in September.
Moisture had a significant effect on the early season forage availability. With above normal moisture in March 2008, switchgrass produced significant biomass by mid-April. In 2009, however, growth was delayed by two weeks due to drought conditions. Over the growing season, forage biomass increased from 1,500 pounds per acre to 14,000 pounds per acre (Figure 1). Changes in weather conditions in 2008 and 2009 also altered the amount of forage available at a given point in time, but by the end of each season there was no significant difference in forage biomass availability between the two years. The majority of forage biomass was realized before the end of July, so timely moisture and temperature conditions between March and July are critical to ensure good yields.
The crude protein content of switchgrass ranged from a high of 17 percent in the early growing season to a low of 4 percent at forage maturity (Figure 2). Total digestible nutrients and dry matter digestibility also decreased as plants matured. Total digestible nutrients ranged from 63 percent in the early season to 55 percent at forage maturity. Dry matter digestibility ranged from 74 percent in the early season to 50 percent at forage maturity. High crude protein, total digestible nutrients and dry matter digestibility in April indicate high quality forage during the early growing season. Early season forage gives producers the option to hay or graze it early, then harvest the regrowth at the end of September for use as a biofuel feedstock. Depending on your market endpoint in a hay production enterprise, you can adjust your harvest timing to either maximize biomass with average quality or lower biomass with higher quality.
For the sustainability of any crop production enterprise, always have your soils tested and apply the required nutrients for your yield goals.