Agronomic use of calcined christmas island iron/aluminium phosphates i. field trials

Abstract

Christmas Island "c" ore when calcined at 550°c contains up to 24% aluminium and iron and 15% phosphorus which is not water-soluble but is up to 95% soluble in neutral ammonium citrate. Samples vary in total phosphorus content and in the percentage of phosphorus soluble in neutral ammonium citrate, depending on the proportions of crandallite, millisite, and apatite in the "c" ore sample. In field trials at Otara finely ground calcined "c" ore-"Calciphos"-gave yields equal to or slightly less than those obtained from superphosphate on both limed and unlimed plots at equal rate of applied P. Yields with a mixture of Calciphos powder and mature superphosphate (1: 1) were equal to, or better than, those from superphosphate alone. Pelletising the finely ground Calciphos reduced pasture responses to 41 % of those obtained from granulated superphosphate. Materials containing the highest percentage of phosphorus soluble in neutral ammonium citrate d(' not necessarily give highest yields, indicating that other factors besides the neutral ammonium citrate solubility may be involved.

Field evaluation of pelletised calcined and insoluble residue of Christmas Island ‘C’ phosphates

“…They suggested that 10% bentonite may be necessary for breakdown to give satisfactory plant responses. Buchan et al (1970) confirmed in pot trials that only pellets with 10% bentonite disintegrated completely in the soil, and Muller (1970) reported that, in a field trial, pelletised Calciphos with 8% bentonite gave pasture yields of 61% of those obtained from superphosphate. However, at that time, the higher cost of producing bentonite pellets relative to the lower cost of phosphate rock was not considered economical.…”

A glasshouse comparison of 6 phosphate fertilisers

“…Although oflittle agronomic value in the raw state, calcination at 550·C increases the agronomic performance of this material. Calciphos has been evaluated extensively in both the glasshouse and the field in New Zealand (Doak et al 1965;Buchan et al 1970;Muller 1970).…”

I. Introduction and design of experiments

“…Nauru Island rock phosphate was considerably less effective, Doak et al (1965) showed that C-grade Christmas Island rock phosphate, which contains crandallite and millisite as well as apatite and is unsuitable for the manufacture of superphosphate by conventional means, could be calcined at about 450"c with resultant degradation of the crystal lattices and enhanced solubility of the phosphate content. Although Muller (1970) and Buchan et at. (1970) found that this finely ground CCIP gave yields equal to or slightly less than superphosphate in field and pot experiments, Elliott (1967) concluded from results offield trials carried out by the New Zealand Department of Agriculture that CCIP was only half as effective as superphosphate when compared on an equal phosphate content basis.…”

“…This discrepancy would appear to be associated with the application rate and the position on the phosphate response curve at which the materials were compared. On closer examination, Muller's (1970) Karlovsky (1976) compared CCIP with superphosphate (annual applications on an equal phosphate basis) in a 5-year trial on permanent pasture on Horotiu sandy loam (a highly phosphate retentive yellow-brown loam). Although the yield from CCIP in the first year was only 41% ofthe yield from superphosphate, it improved with time, and by the fifth year it yielded 84% as much as superphosphate.…”