Harvest Management of Switchgrass for Biomass Feedstock and Forage Production

Abstract

AbstractSwitchgrass (Panicum virgatum L.), a warm‐season perennial grass native to North America, has potential as a biomass energy crop. Our objective was to develop harvest management recommendations for biomass feedstock and forage production. ‘Alamo’ switchgrass was established in 1992 at Stephenville and Dallas, TX. Four harvest frequencies (one to four cuts per year) and three final autumn harvests (Sept., Oct., or Nov.) were imposed from 1993 to 1996. Tiller densities were counted each spring. Neutral detergent fiber (NDF) and crude protein (CP) concentrations were measured in 1993 and 1994. Concentrations of NDF were lowest (avg. = 640 g kg−1) and of CP (avg. = 110 g kg−1) were highest in May‐harvested biomass. Forage quality of regrowth decreased with age, reaching NDF concentrations of 790 g kg−1 and CP of <20 g kg−1. Total seasonal yields decreased as harvest frequency increased; however, a severe drought reversed this trend at Dallas in 1996. The highest yields (15–20 Mg ha−1) occurred with a single harvest in mid‐September. Delaying the final harvest until November reduced yields. Harvest date and frequency did not affect tiller density, although tiller density decreased from 900 to 650 and 630 to 310 m−2 at Dallas and Stephenville, respectively, during 1994 to 1997. Thus, a single mid‐September harvest should maximize biomass yields in the south‐central USA. A two‐cut (spring‐autumn) system may allow a farmer to use initial growth as forage and the regrowth for biomass, but total yields would be reduced. More frequent harvests would reduce yields further.