Switchgrass Winter Yield, Year-Round Elemental Concentrations, and Associated Soil Nutrients in a Zero Input Environment

The maximum biomass yield of switchgrass (Panicum virgatum L.) usually is achieved with one seasonal autumn harvest. However, information is limited on the influences of winter harvesting on annual biomass yield and on quality parameters impacting conversion into bioethanol. Accordingly, the objectives of this study were to assess: (i) yield of standing field cured biomass at monthly intervals through winter, (ii) year-round elemental composition of biomass, and (iii) associated year-round soil nutrient status. An unfertilized 'Kanlow' switchgrass planting established in 1998 was used for this study conducted from November 2007 to October 2010. The experimental treatment was monthly harvest from November to the following March and year-round monthly sampling of biomass (except April) and soil for chemical analyses. The 3-yr mean dry matter yield of winter harvests was 5.94Mg ha(-1), ranging from 3.88 Mg ha(-1) in the winter of 2007-2008 to 7.55 Mg ha(-1) in 2009-2010. Monthly biomass yield differences were significant in Years 1 and 3 but not in Year 2. Concentrations of biomass elements and soil nutrients changed with various degrees over the 3 yr. Concentrations of ash, cell wall components, and mineral nutrients, except P, K, and S, did not change appreciably across winter months. Early winter harvests resulted in less yield loss compared to late winter harvests. These findings will be valuable in harvest management for switchgrass biomass production.