The fractionation of phosphorus in two soils of different age : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Agricultural Science with Honours in the University of Canterbury

Abstract

Phosphorus is one of the most important plant nutrients and is of considerable importance in maintaining a high level of soil fertility. The large importations of phosphatic fertilizers into the country have been aimed at remedying the general poverty of this element in New Zealand soils. Requirements are increased by the fact that many soils are strongly phosphate "fixing" e.g., the Taranaki yellow brown loams. On the other hand, there are some soils such as the recent soils on the east coast of the South Island, whose fixing capacity is virtually negligible. But these soils have other problems. In spite of having a large reserve of Truog phosphate, soils of the potato growing are as of the Waimakariri series respond to phosphate fertilization. Davies (1960 ) and Grigg (1961, 1965) have found that the Truog reagent (Truog, 1930) is able to dissolve calcium-bound primary soil phosphorus of low plant availability and consequently erroneously high results are obtained with these soils. It was thought that much of the calcium-bound phosphorus could be present in the coarse sand fractions of these soils which might not readily dissolve and be available for plant uptake due to the low annual rainfall of only 26 inches. Therefore it was decided to fractionate the inorganic phosphorus in the mechanical soil separates from two profiles; one younger and another older than the Waimakariri. Before presenting details of the materials and methods used in the study and the results obtained , the relevant literature is reviewed in order to assess the nature and conditions of occurrence of the various categories of phosphorus in soils and mechanical soil separates and also the factors governing their extraction.