Effects of late-season sheep grazing following early-season steer grazing on population dynamics of sericea lespedeza in the Kansas Flint Hills

Mature ewes were used in a 4-yr study to evaluate effects of intensive late-season sheep grazing on vigor of sericea lespedeza in native tallgrass prairie. Pastures (N = 8; 31 ± 3.6 ha) infested with sericea lespedeza (initial basal frequency = 1.4%) were assigned randomly to one of two treatments: early-season beef steer grazing (1.1 ha/steer; initial BW = 258 ± 34 kg) from April 15 to July 15 followed by no grazing for the rest of the year (control; STR) or steer grazing from April 15 to July 15 followed by intensive grazing by mature ewes (0.2 ha/ewe; SHP) from August 1 to October 1. Ewes (initial BW = 65 ± 3.1 kg) were assigned randomly to graze four of eight pastures; remaining pastures were not grazed from August 1 to October 1. Vegetation responses to treatment were measured along four permanent 100-m transects in each pasture. Herbivory on sericea lespedeza was monitored weekly in each pasture from July 21 to October 7. Herbivory on sericea lespedeza in SHP and STR after steer grazing and before sheep grazing was not different (P = 0.51). In contrast, sericea lespedeza herbivory following sheep grazing was greater (P < 0.01) in SHP than in STR. Herbivory of individual sericea plants was greater (P < 0.01) in SHP than in STR by the end of week 1 of the sheep-grazing period (10.6% vs. 0.5%); moreover, herbivory on sericea lespedeza steadily increased (P ≤ 0.01) such that 92.1% of sericea lespedeza plants were grazed in SHP compared to 1.4% in STR by week 8 of the sheep-grazing period. Whole-plant DM weight of sericea lespedeza at dormancy was less (P < 0.01) in SHP than in STR. Additionally, annual seed production by sericea lespedeza was less (P < 0.01) in SHP than in STR (114 vs. 864 seeds/plant). Pasture forage biomass was not different (P = 0.76) between SHP and STR after the steer-grazing period. Conversely, STR had more (P < 0.01) residual forage biomass than SHP at the end of the sheep-grazing period. Growth performance of beef steers grazing from April 15 to July 15 annually was not different (P ≥ 0.59) between treatments. Our results were interpreted to suggest that intensive late-season grazing by sheep decreased vigor of sericea lespedeza. Late-season sheep grazing decreased forage biomass by 904 kg DM/ha compared with late-season rest; however, residual biomass was adequate to prevent soil-moisture loss and erosion during the dormant season.