Laboratory study of the behaviour of added phosphate in an allophanic soil : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Soil Science at Massey University, New Zealand

Abstract

A feature in the maintenance of high producing pastures, on the yellow-brown loam soils in Taranaki, is the need for high annual rates of phosphatic fertilizer application. Burgess and Davies (1951) in some early investigations into soil fertility problems in Taranaki noted that the yellow-brown loams could apparently accumulate large amounts of phosphate in a form which was difficult for plants to extract. Consequently to ensure adequate plant phosphate nutrition large annual dressings of superphosphate are recommended for high producing pastures on these soils. This high phosphate-retaining property has been attributed to the presence of active aluminium supplied by allophane, the predominant clay mineral in these soils (Saunders 1959 (b)). The only recent intensive study to be made on phosphate relationships in the yellow-brown loams is that of Saunders (1959 (a)(b)(c)) who carried out chemical fractionation of the phosphate in New Plymouth black loam, a soil which may be considered as representative of the group as a whole. His sampling sites were on areas of different topdressing histories, and although he was able to draw certain conclusions in respect of the trends of phosphate fixation this approach does not provide any information on the shorter term fate of applied phosphate. Information of this kind is, however essential if a rational explanation of the established need for substantial annual additions of phosphate to these soils, is to be forthcoming. [From Introduction]