Harvest Frequency and Nitrogen Effects on Yield, Chemical Characteristics, and Nutrient Removal of Switchgrass

Harvest frequency (HF) and fertilizer effects on biomass production, nutrient removal, and ethanol yield must be understood to help guide management decisions in switchgrass (Panicum virgatum L.) production. This 4-yr study quantified yield and chemical composition responses of Alamo switchgrass to factorial combinations (4 x 2) of four HFs (harvesting one, two, three, or six times annually) and two N application rates (80 and 160 kg N ha(-1)) in a randomized complete block design experiment with three replications. In all years, yields decreased linearly with HF. In the one-cut HF, yield increased from 8.8 in Year 1 to 14.7 Mg ha(-1) in Year 3 and plateaued thereafter. For the two-cut HF, yield was similar across years, averaging 10 Mg ha(-1), but for the three-and six-cut HFs, yield increased from Year 1 to Year 2 and declined by Year 4. Nutrient concentration increased with HF, while nutrient removal responses fluctuated among elements. Acid detergent fiber, neutral detergent fiber, hemicellulose, cellulose, and lignin concentrations decreased with increasing HF, but there was no effect of N rate. In Years 1 and 2, theoretical ethanol production (TEP) was similar between the one- (3.7 kL ha(-1)) and two-cut HFs (4.2 kL ha(-1)) but decreased as the HF increased to three (2.6-3.4 kL ha(-1)) and six cuts (1.4-2.5 kL ha(-1)). In Years 3 and 4, TEP decreased linearly with increasing HF. Greater HF resulted in reduced feedstock yield, quality, ethanol yield, and production, but N application rate did not have any effect.