Studies on soil phosphorus III. Phosphorus fractionation as a fertility index in South Australian soils

Extract

A simplification of Ghani's method for the fractionation of soil phosphorus has been used to study relationships between soil and plant phosphorus in field and pot-culture experiments.

In pot-culture experiments with red-brown earth soils (pH 5·6–6·1) wheat derived approximately 60% of its phosphorus from the fraction of soil phosphorus soluble in 2·5% acetic acid-1% 8-hydroxyquinoline and 30% from the inorganic fraction soluble in 0·1 n-sodium hydroxide, even although the amount of acetic acid soluble phosphorus present in these soils was only about half that present as inorganic alkali soluble. Very little use was made of organic phosphorus.

In field experiments with similar soils there was a correlation between the percentage phosphorus in the plant material and the acetic acid soluble, the inorganic alkali soluble, and the sura of these two fractions of soil phosphorus. The sum of these two fractions was also correlated with the amount of phosphorus taken up by the crop.

In pot-culture experiments with a wider range of soil types there was good correlation between the total extractable inorganic soil phosphorus and both the phosphorus content of the plant and the phosphorus uptake. Correlations between individual inorganic extractable soil phosphorus fractions and plant phosphorus were influenced by the pH of the two groups of soils examined.