Fig. 4.

Relationship between crop relative yield (RY) and pH with the effect of phosphorus (⬤ +P, ○ -P) for spring barley (a, d), winter triticale (b, e) and winter wheat (c, f) at the Rothamsted (a, b, c) and Woburn (d, e, f) sites; regression fit for + P are given with solid lines, for -P with dashed lines and a single dotted line where there was no difference between + P and -P. For actual crop yield (t ha⁻¹) refer to Table 6, Table 7.