Fig. 2. The relationship between first cut forage dry matter yield and fertilizer N. Data from Doyle, Lookout, and Ft. Jones in 2005 (2-cut sites) were pooled. Data from McArthur in 2005 and Susanville and Montague in 2006 (3-cut sites) were pooled. The model was fitted on data from all plots while symbols illustrate mean dry matter yield response for a given N treatment.

Image from Forage and Grazinglands article:
Assessing Nitrogen Fertilization Needs for Irrigated Orchardgrass in the Intermountain Region of California