Questions have been raised about whether herbaceous productivity declines linearly with grazing or whether low levels of grazing can increase productivity. This paper reports the response of forage production to cattle grazing on prairie dominated by Kentucky bluegrass (Poa pratensis L.) in south-central North Dakota through the growing season at 5 grazing intensities: no grazing, light grazing (1.3 ± 0.7 animal unit months [AUM] · ha−1), moderate grazing (2.7 ± 1.0 AUM · ha−1), heavy grazing (4.4 ± 1.2 AUM · ha−1), and extreme grazing (6.9 ± 2.1 AUM · ha−1; mean ± SD). Annual herbage production data were collected on silty and overflow range sites from 1989 to 2005. Precipitation and sod temperature were used as covariates in the analysis. On silty range sites, the light treatment produced the most herbage (3 410 kg · ha−1), and production was reduced as the grazing intensity increased. Average total production for the season was 545 kg · ha−1 less on the ungrazed treatment and 909 kg · ha−1 less on the extreme treatment than on the light treatment. On overflow range sites, there were no significant differences between the light (4 131 kg · ha−1), moderate (4 360 kg · ha−1), and heavy treatments (4 362 kg · ha−1; P > 0.05). Total production on overflow range sites interacted with precipitation, and production on the grazed treatments was greater than on the ungrazed treatment when precipitation (from the end of the growing season in the previous year to the end of the grazing season in the current year) was greater than 267.0, 248.4, 262.4, or 531.5 mm on the light, moderate, heavy, and extreme treatments, respectively. However, production on the extreme treatment was less than on the ungrazed treatment if precipitation was less than 315.2 mm. We conclude that low to moderate levels of grazing can increase production over no grazing, but that the level of grazing that maximizes production depends upon the growing conditions of the current year.
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Vol. 60 • No. 6