Figure 3

3-dimensional design space defined by NH ₄ ⁺:K⁺, NH ₄ ⁺:K⁺ amount, and NO ₃ ^- amount. The experimental region for this study is a selected slice, shown in grey with treatment points in red, through the 3-dimensional design space where all points on the plane have a pH of 5.8 – pH increases above the plane and decreases below it.