Biomass vs. quality tradeoffs for switchgrass in response to fall harvesting period

• The highest biomass yield was recorded from harvests in October.
• The highest combustion quality was achieved with the latest harvest in mid-November.
• Moisture content was reduced with delaying the harvest yet direct bailing was impractical.
• Non-structural carbohydrates were higher in November harvests.
• Harvesting in early-November could ensure high quality biomass production.

Switchgrass (Panicum virgatum L.) is perhaps the most promising crop for bio-energy production. Optimal time of harvest may be critical for producing high-yielding switchgrass of suitable quality for combustion. In general, delayed harvest has been suggested to improve switchgrass quality through reducing ash, moisture and mineral content however, postponing harvest may have negative impact on biomass yield. An experiment was conducted on a Hadley fine sandy loam soil in South Deerfield, MA during 2010 and 2011 to determine optimum fall harvest time (mid-September, early-October, mid-October, early-November, mid-November) for improving switchgrass (cv. Cave-in-Rock) quality without significant reduction in biomass yield. Non-structural carbohydrates (NSC) were also measured as an indicator of crop health. In both years, delaying in harvest decreased ash and mineral content while biomass yield was also reduced. Maximum biomass yield (11.4 Mg ha−1) was obtained from mid-October harvest in 2010 whereas; the highest biomass production was obtained from early-October (10.0 Mg ha−1) in 2011. Switchgrass harvested in mid-September contained the highest moisture (55%), ash (47 g kg−1), and nitrogen (N) (3.8 g kg−1). Overall, sucrose was the most abundant sugar among NSC and reached its peak concentration (5.3 mg g dry matter−1) when crop was harvested in November in 2010. Results obtained in this study indicated that optimal time of harvest varies from early October to early-November depending upon the weather condition.