"WW B. Dahl", a perennial old world bluestem (OWB) grass, has been promoted as a forage suitable for dryland grazing. Dryland grazing of OWB is however inherently risky economically and ecologically, and may not be sustainable while remaining profitable. In this paper we develop a biological and economic single-season model of dryland grazing given production and price uncertainty, and identify a stocking rate that maximizes expected net revenue, subject to a sustainability constraint. We then simulate the distribution of net revenues, and find that probability of loss is greater than 35%, and median profit is roughly $30/ha.