A pedological study of phosphorus in 12 soils derived from granite

Abstract

Chemical analysis of 12 soil profiles on granite showed that all except two had lost phosphate by leaching. The loss of phosphorus from each profile is calculated in grams per sq centimetre of profile surface, and as a percentage of the amount originally present. Three methods of calculation are used, each being based on one of the following assumptions as to the changes which take place on rock weathering: that there is (a) no change in weight, (b) no change in volume, (c) no loss of zirconium. The three methods are generally consistent in showing which soils are the most leached and which are the least leached. The estimated loss of phosphorus from each profile depends on which assumption is made. There is no simple correlation between the loss of phosphorus and the present rainfall. Reasons which are suggested are that the soils differ in age, in level of organic matter, and possibly in the rates of weathering of the parent rocks. Up to two-thirds of the phosphorus retained in the soil is chemically bound by the free oxides of iron and aluminium.