Relationship between Base Saturation and Crop Response to Phosphate in Acid Soils

Abstract

IN an attempt to relate phosphate responses in the field with soil analyses, the most significant correlations I have yet obtained have been between response and the percentage saturation of the base exchange capacity. It should be noted that all the soils, with one exception, lay within the range pH 4.7–6.3. In three groups of experiments (fifty-six observations) on wheat, grass and millet, the regressions of crop response (percentage increase in yield due to superphosphate over control) on the percentage saturation of the base exchange capacity were highly significant (P < 0.01) in spite of the fairly wide variation in soil types. The relationship was an inverse one, and the equations indicated that phosphate responses are not to be expected when base saturation exceeds about 80 per cent. A similar relationship was found between response and exchangeable calcium expressed as a percentage of exchangeable calcium plus exchangeable hydrogen, that is, in units similar to the percentage saturation of the base-exchange capacity.