Do yield and quality of big bluestem and switchgrass feedstock decline over winter?

Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerdardii Vitman) are potential bioenergy feedstocks for thermochemical platforms. Feedstock storage, fall harvest constraints, and environmental benefits provided by perennials are rationales for developing localized perennial feedstock. However, little information is available on mineral and thermochemical properties of native species or on the impact of delaying harvest until spring. Objectives of this study were to compare the feedstock quantity and quality of grasses harvested in the fall (Fall Harvest) or the following spring (Spring Harvest). It was hypothesized that biomass yield may decline, but the feedstock quality would increase due to leaching of minerals. Big bluestem and switchgrass yields differed among years, but not by harvest timing between fall and the subsequent spring as both grasses produced an average 5.7 Mg ha-1 yr-1. Thermal quality properties analysis for both grasses detected significant decreases in ultimate C, volatile C, fixed C, H, and O concentration and subsequently a decline in caloric content between Fall and Spring Harvest times. However, these observations were attributed primarily to one very muddy spring harvest, as the effect was not observed between Harvest time pairs in other years. Potassium and Cl concentration of both grasses declined between Fall and Spring. Feedstock quantity and quality were maintained or improved by K reduction most years making spring harvest a viable option if fall conditions delayed harvest. However, late snows and wet spring conditions can also hamper early field access; thus, we recommend fall harvest when feasible and storage space is available.