Harvest frequency and harvest timing following a freeze event effects on yield and composition of switchgrass

Abstract

AbstractConstant supply of biomass from the field is limited by the seasonality of production of warm‐season grasses in the transition U.S. region. Delaying harvest after occurrence of freeze may be an alternative to extend the biomass supply period of switchgrass (Panicum virgatum L.) in North Carolina. The objectives of this study were to evaluate the effects of harvest frequency (HF) and harvest timing at the end of the growing season (HT) on switchgrass biomass yield, nutrient (N, P, and K) removal, and dry matter (DM) and ash concentrations. Treatments were the factorial combination of two HF (clipped once [1X] or twice [2X] per season) and three HT (before freeze in October, after first freeze in November, and late winter in February). Delaying harvest after occurrence of freeze did not affect total annual biomass yield for the 2X treatment (average of 15.5 Mg ha−1), whereas for 1X yield declined from 14.4 to 10.1 Mg ha−1 when harvest was delayed from October to February. Ash concentration declined from 29 g kg−1 in October to 14 g kg−1 in February. The DM concentration level reached in February was lowest (893 g kg−1) and it would be considered safe for storage of biomass. Nutrient removal was consistently greater for 2X than 1X (ranging from 43 to 137, 3.6 to 25.1, and 54 to 213 kg ha−1 for N, P, K, respectively). Delaying harvest of switchgrass after a freeze event is feasible when clipping twice a year to extend the window of biomass supply.