MANAGEMENT OF SWITCHGRASS FOR FORAGE AND SEED PRODUCTION

Management of switchgrass (Panicum virgatum L.) for both forage and seed would improve the diversity of options livestock producers have for their stands. Our objective was to evaluate how timing of the forage harvest and N applications can be used to manage switchgrass for both forage and seed from the same stand. Switchgrass forage was harvested in late May (prior to stem elongation) or mid-June (early boot stage) or left uncut and treated with either a single application of 88 kg N ha-1 in the spring or 4-weeks after green-up, or split applications of 44 kg N ha-1 in the spring and 44 kg N ha-1 following defoliation. The late May harvest gave lower yields of higher quality forage whereas the mid-June harvest produced greater yields of lower quality forage. Both the late May and mid-June harvest increased total tiller density compared to uncut plots, but a mid-June harvest decreased reproductive tiller density. Application of N following defoliation increased both total tiller density and reproductive tiller density but the response was small with a mid-June harvest. A mid-June harvest reduced both seed yield and 100-seed weights all 3 years. A late May harvest reduced same-year seed yields and 100-seed weights in 1991 only, when the harvest was taken after stem elongation had initiated. Application of N following defoliation stimulated plant regrowth, enhancing same-year seed yield. Harvesting switchgrass for forage in the spring prior to stem elongation followed by a post-harvest N application of 44 kg N ha-1 allows producers to manage switchgrass for both forage and seed.