Long-term responses in the yield of Eastern Gamagrass [Tripsacum dactyloides (L.) L.] to nitrogen fertilizer under two harvest regimes in the United States

Eastern Gamagrass [ Tripsacum dactyloides (L.) L.] is a perennial C₄ grass with potentially high productivity. Intensive management through the application of nitrogen (N) fertilizer and frequency of cutting, however, may be required to maximize its potential for forage production. This study determined the long-term and residual responses of Eastern Gamagrass in terms of dry matter (DM) yield and tiller density to three annual application rates (0, 50 or 100 kg ha⁻¹) of a N-fertilizer solution applied by broadcasting or knife placement for 5 out of the 10 years of the study, and harvested using one-cut or two-cut regimes. Application of N-fertilizer increased total DM yield in the 5 years of N applications by 0·44 with the first increment of 50 kg N ha⁻¹, and by an additional 0·15 with the next increment of 50 kg N ha⁻¹. In the first year that directly followed N-fertilizer applications, DM yield was 0·175 higher than the no fertilizer treatment when 50 kg ha⁻¹ had been previously applied and a further 0·16 higher when 100 kg ha⁻¹ had been previously applied. Dry matter yields were greater from the one-cut than the two-cut regime only in years when no N-fertilizer was applied. Knife placement of N-fertilizer increased total DM yield only at 100 kg N ha⁻¹. Tiller densities were generally higher under the one-cut than the two-cut regime, particularly when N-fertilizer was broadcast. The application of N-fertilizer increased herbage production, especially when responses in the year subsequent to application are considered.