Productivity of Kentucky Bluegrass Pasture Grazed at Three Heights and Two Intensities

Abstract

Sward height before grazing and amount of forage harvested affect production, composition, and utilization of rotationally stocked pasture. In this 3‐yr field study, yearling steers (Bos taurus L.) grazed 400‐m2 plots of Kentucky bluegrass (Poa pratensis L.)–white clover (Trifolium repens L.) pastures every time sward height reached either 11.8 cm (short), 13.7 cm (medium), or 15.3 cm (tall). Plots were grazed with enough steers to remove either 50 or 60% (grazing intensity) of the herbage mass in 4 h. The experimental design was a 3 × 2 (height treatment × grazing intensity) factorial with four replications. Sward heights before and after grazing periods were measured. Herbage mass, apparent growth rate, herbage removed, rejected area, and percent utilization were calculated. Average herbage mass before grazing ranged from 1855 to 2350 kg dry matter (DM) ha−1. Average herbage mass after grazing varied from 855 to 1060 kg DM ha−1. Apparent herbage growth rate (54 kg DM ha−1 d−1) and herbage removed (7520 kg ha−1) were highest on the short height treatment with low grazing intensity (50% removal). Assuming a sigmoidal growth curve, maximum apparent growth rate occurred at 10.5‐cm sward height. More than twice as much herbage was removed in the wettest year compared with the driest. In the dry year, height and intensity of grazing had little effect on herbage production. Thus, the benefits farmers can expect from more intensive grazing management will be more evident in a year of good growth.