Optimal Fall Harvest Time for Production of High-Quality Switchgrass Grown for Combustion.

Information on optimal fall harvest time of switchgrass (Panicum virgatum L.) grown for combustion in Northeastern region is limited. The objective of this study was to develop harvest management recommendations for the production of switchgrass in the region. Seasonal harvest time from senescence, after seed production, to killing frost affects yield and feedstock quality. A field study with five harvest times and four replications was conducted during 2010 and 2011 growing seasons. Established stands of ‘Cave-in-Rock’ were harvested twice a month from mid-Sept to mid-Nov. Switchgrass dry matter yield (DMY), ash, total nitrogen (N), mineral content, and energy content in the feedstock and non-structural carbohydrates in the roots at the time of each harvest were measured. Maximum DMY was obtained in early to mid-Oct ranging from 10-11 Mg ha^-1. Total ash as well as macro-nutrients including N, phosphorus, potassium, decreased linearly as harvest was delayed from mid-Sept to mid-Nov (killing frost). Sucrose levels of the root system significantly increased in mid-Nov.  The unit energy content in the feedstock decreased linearly from mid-Sept to mid-Nov ranging from 7366-10,696 J g^-1.