Forage Production Characteristics and Performance of Growing Beef Heifers Grazing Native Warm-Season Grass Mixtures

Abstract

A 2-yr study was conducted at Black Belt Research and Extension Center in Marion Junction, AL to evaluate the effect of nitrogen (N) fertilizer application rate on forage production, nutritive value, sward characteristics, and performance of beef heifers grazing a mixture of big bluestem, little bluestem, and indiangrass. Six, 2-ha plots were randomly assigned to one of two treatments (0 or 67 kg N ha-1 applied in early April; n = 3 replications per treatment). Paddocks were continuously stocked with 4 weaned Angus x Simmental beef heifers from late May/early June through mid-to-late August during 2018 and 2019, respectively. Additional put-and-take cattle were used to manage forage to a target height of 38 cm. Forage mass and canopy sward heights were collected every 2 wk during the trial. Visual ground cover ratings, canopy light interception, and botanical composition were measured at the beginning and end of the trial in each yr. Hand-plucked samples were collected every 2 wk during the grazing trial to determine forage nutritive value. Data were analyzed using the PROC MIXED procedure in SAS 9.4, and differences were declared significant when P ≤ 0.05. Nitrogen-fertilized NWSG had greater CP concentration (P < 0.0001), sward heights (P = 0.0003), and canopy light interception at the beginning of the season (P = 0.0049) than unfertilized paddocks. Unfertilized NWSG had greater digestibility than those fertilized with N (P = 0.0004). However, there were no differences (P ≤ 0.05) among N-fertility treatments for mean forage production (mean: 4489 kg DM ha-1 ), heifer ADG, or BCS across the 2-yr study. Forage production and sward heights peaked in June, then decreased through mid-tolate summer. Botanical composition data indicated that indiangrass decreased from 64% to 61% (P = 0.0022) and weed pressure increased from 11% to 15% (P = 0.0064) across the summer grazing season. Canopy light interception decreased by 51.4% from early June to August in fertilized NWSG and 26.4 % in unfertilized paddocks, respectively. These data illustrate that NWSG systems may provide a viable grazing system in the summer months under reduced N inputs.