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The relationship between grain yield (t ha−1) and soil pH for (a) spring oats in 1975 (⬤), 1977 (○), 1981 (▾), 1982 (△) and (b) spring beans in 1963 (⬤), 1964 (○), 1989 (▾) and 1990 (△) at Rothamsted; in (b) the regression curves represent significantly different fits for separate years for spring beans.
