The use of chemical data in the prognosis of phosphate deficiency in soils

Abstract does not appear. First page follows.

Lack of Correlation Between Plant Growth and Acid-Extractable Phosphate

Soil chemists have long recognized that there is a certain rationale in extracting soils with acids to determine the capacity of soil particles for releasing ions to the plant. Unfortunately, attempts to correlate the actual amounts of given ions released by acids in the laboratory with the amounts of such ions absorbed by plants have not been highly successful.

Two general types of explanation might account for the discrepancy. The first of these is that, although the release of H ion to the soil by plants and microörganisms is always quantitatively important, the plant can, by absorbing from the liquid phase, shift the equilibrium between the liquid and solid phase without a material change in the H ion concentration of the system. Ions thus released independently of evolution of acid by the plant become a part of the soil solution and can be absorbed by the plant. Moreover, H. Jenny5 has shown that the merging of the swarm of ions in the electrical double layer of the soil particle with a similar system at the root-hair surface, is sufficient to cause the removal of an exchangeable cation from the soil to the root hair and that there is no necessity for postulating the presence of a discrete intervening layer of soil solution or the excretion of acids by the plant to account for acquisition of such ions by plants. We suggest that this type of exchange could also take place if the soil particles and root-hair surfaces carry mutually exchangeable anions.