The chemical composition of the soil in a factorial experiment with citrus. I. Exchangeable metal cations and their effect on the cation content of citrus

Abstract

In a factorial field experiment with citrus it was found that application of ammonium sulphate caused a greater proportionate reduction in the exchangeable calcium of the soil than in the exchangeable potassium. Short-term laboratory experiments with virgin soil, to which ammonium was added, suggested that at least two factors were involved. If solutions of high electrolyte concentrations were added, a greater release of exchangeable calcium than of potassium occurred, relative to the amounts of these ions originally present in exchangeable form. Secondly, a release of potassium from non-exchangeable to exchangeable form also occurred. In the 0–4 in. layer of the field experiment, exchangeable magnesium was reduced in the same proportion as exchangeable calcium. In the 4–12 in. layer, exchangeable magnesium was reduced relatively more than calcium. The same trend was apparent in laboratory experiments. In one experiment, for example, the original amount of magnesium was reduced by 76 per cent., and calcium by 66 per cent. A comparison between cultural treatments showed that the potassium content of the soil from a bare surface treatment was much lower than that from treatments with cover crops. The changes in soil composition had no appreciable effect on the cation content of citrus leaves, and some reasons for this are discussed.