Figure 2: The effect of inorganic N fertilizer and biosolids on yield and grain protein content of three wheat market classes at Lind (a), Davenport (b), and Pullman (c), Wash in 2008. The horizontal axis (N rate) is the same for Lind and Davenport but higher for Pullman. Due to differences in grain yield, the vertical axis is different for Lind relative to Davenport and Pullman. Where indicated by the regression line, quadratic or linear responses are significant at . If no regression line is included the relationship was not significant ( ). * and ** indicate significant differences at the 0.10 and 0.05 level, respectively, between inorganic N and biosolids treatments at that inorganic nitrogen and biosolids rate.