Maximizing Seed Production in Eastern Gamagrass

Use of eastern gamagrass (Tripsacum dactyloides L.) for grazing or cut forage has been partially limited because of indeterminate inflorescence development combined with low seed yields and high seed costs caused by high seed shattering. This study was conducted to observe the influence of N rate and defoliation on inflorescence appearance, seed loss, and viability of harvested seed in two cultivars of eastern gamagrass at Boone, IA, in 2000 and 2001. Treatments included application of N at 0, 56, 112, 224 kg ha(-1) and spring, fall, and no defoliation. Cultivar had the greatest influence on seed yield. 'Pete' produced greater total numbers of terminal and lateral inflorescences and cupules than 'Iuka' in both years. Reductions in seed production occurred with spring defoliation in luka for the first year of the study and Pete during both years. In 2000, seed on lateral inflorescences was decreased 20% during the peak seed load. In 2001, seed yield for spring-defoliated plants of Pete was less than that of fall-defoliated plants, but not significantly different from nondefoliated plants. Addition of 56 kg ha(-1) N increased seed load in the second year of the study. Optimal harvest time occurred approximately 2 wk after terminal cupules began shattering. Seed harvested 1 wk earlier than this had 5 to 15 percentage points more immature seed. Seed yield was 13 to 20% less if harvests were taken 1 wk later than the optimal date.