Defoliation Effects on Production and Nutritive Value of Four Irrigated Cool‐Season Perennial Grasses

Irrigated cool‐season perennial grasses are becoming an important complementary forage source in the Central Plains. A study was conducted to evaluate effects of clipping stubble height on dry matter (DM) production, growth rate, tiller density, and nutrient content of smooth bromegrass (Bromus inermis Leyss.) orchardgrass (Dactylis glomerata L.), creeping foxtail (Alopecurus arundinaceus Poir.), and meadow bromegrass (Bromus riparius Rhem.) under irrigated conditions on a Cozad silt loam soil (fine‐silty, mixed, mesic Typic Haplustoll). Clipping treatments (35‐cm canopy height cut to 7‐, 14‐, and 21‐cm stubble heights) were applied to monoculture plots of these species for two growing seasons in a randomized complete block design. Stubble height effects on total DM production varied by species (P < 0.05). For orchardgrass and meadow bromegrass, DM production was similar at the 14‐ and 21‐cm stubble heights (22.22 Mg ha−1), but significantly greater than production at the 7‐cm stubble height (14.03 Mg ha−1). In contrast, DM production of smooth bromegrass and creeping foxtail was significantly greater at each successively higher stubble height. End‐of‐season tiller density of the 7‐cm stubble height treatment was about 50% of the tiller density of the 14‐cm and 21‐cm stubble height treatments. Stubble height effects on nutritive value varied by species and clipping period. Stubble height did not affect crude protein (CP) content of creeping foxtail, but CP was lower at the 7‐cm height for the other species. Defoliation strategies that maintain adequate residual herbage will optimize production of nutrient dense forage and maintain tiller density.