Vegetation dynamics in nitrogen‐fertilized versus mixed legume‐smooth bromegrass pastures interseeded with sorghum‐sudangrass

Abstract

AbstractInterseeding annual warm‐season grasses may increase forage and pasture productivity. From 2017 to 2019, we conducted a grazing experiment that examined smooth bromegrass (Bromus inermis Leyss.) pasture responses to interseeding sorghum‐sudangrass [Sorghum bicolor (L.) Moench × S. bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet & Harlan]. The experiment had a split‐plot design with six main plots each containing two, 0.60‐ha pasture subplots (i.e., 12 total subplots). The six main plots included three replications each of two pasture types: (A) nitrogen (N)‐fertilized smooth bromegrass (FERT) and (B) mixed legume‐smooth bromegrass [LEG; alfalfa (Medicago sativa L.), red clover (Trifolium repens L.), and birdsfoot trefoil (Lotus corniculatus L.)]. The subplots included sorghum‐sudangrass interseeded and unseeded control treatments. Each pasture subplot, which supported two steers (Bos taurus) from spring through summer, contained six, 0.10‐ha sub‐subplots for rotational stocking. Sorghum‐sudangrass was interseeded after stocking cycle 2 in two of the sub‐subplots in the interseeded subplot each year. Vegetation responses were evaluated in these sub‐subplots and in two adjacent sub‐subplots in the unseeded control subplot. Across years, sampling dates, and subplot treatments, the LEG main plots supported 7% greater forage biomass (2743 ± 102 kg ha−1) and six more grazing days than the FERT main plots (2552 ± 111 kg ha−1). Sorghum‐sudangrass interseeded sub‐subplots, however, had 36% greater forage biomass than unseeded sub‐subplots pre‐grazing in stocking cycle 5. To optimize forage biomass, producers should fertilize in early spring or maintain legumes in smooth bromegrass pastures. Interseeding sorghum‐sudangrass provides an option to increase late‐summer forage biomass.