Fig. 2. Testing of the model for wheat. Fischer (1993), Olesen et al. (2000), and Wuest and Cassman (1992) treatments were nitrogen (N) fertilization rate and timing in irrigated experiments. Olesen et al. (2000) experiments were affected by powdery mildew and Septoria spp. McDonald (1992) treatments were N fertilization rates and site. Halvorson et al. (2004) treatments were fertilization rate, rotation, and year in dryland winter wheat in Akron, CO. Huggins (1991) treatments were N fertilization rates and timing in dryland spring wheat in a Mediterranean climate (Pullman, WA).