Effect of particle size on the avalibility of phosphorus in Nauru rock phosphate, greywacke and basaltic rocks

Abstract

Most of the soils of the world are phosphorus deficient since plant growth is increased by phosphate application.

This situation is particularly true in New Zealand where increased yields from phosphorus are obtained with almost all crops on almost all soil types. Phosphate fertilization is practically essential on pastures for the successful establishment of legume/grass associations and the maintenance of high levels of herbage production by virtue of the ability of phosphate to stimulate legumes which produce the combined nitrogen by symbiosis for the associated grasses.

The important role of phosphorus in primary production, the backbone of the New Zealand economy, is shown by the fact that phosphatic fertilizers are the main fertilizers used, with superphosphate and its derivatives accounting for 90% of the total fertilizer consumed, i.e., 1.5 million tons per annum. Consequently considerable research has been undertaken to investigate the nature and behaviour of soil and fertilizer phosphorus in New Zealand.

The objective of the present study was to evaluate the particle size effects on the availability of phosphorus in Nauru rock phosphate and two rock materials – greywacke and basalt. The effects were measured, in the case of rock phosphate, by chemical solubility tests and plant growth in the glasshouse, and, in the case of the rock materials, by chemical extractions, phosphorus fractionation and fungal growth.