Agronomic use of calcined christmas island iron/aluminium phosphates

Abstract

Glasshouse pot trials with ryegrass, subterranean clover, and radish as indicator plants showed that calcined Christmas Island iron/aluminium phosphates (Calciphos) when finely ground and mixed into the soil gave yields equal to those from the use of granulated superphosphate. Localising the powder in spots significantly reduced the yields only in early harvests. Plant response was greatest to material calcined between 500°c and 700°c, and yields were lower from material calcined below 500'c than from that calcined above 700°c. In pot trials pelletising Calciphos severely reduced yields. Bentonite, smectite, and sulphur were added in varying proportions to Calciphos in an attempt to make pellets which readily disintegrated on moist soil, so making the phosphate more available to plants. The improvement obtained was not sufficient to warrant the extra cost of pellet formulation and decrease in phosphate content.

A glasshouse comparison of 6 phosphate fertilisers

“…The 6 P sources evaluated can be ranked in the following decreasing order of agronomic effectiveness when ryegrass was used: superphosphate ~ NCPR ~ SPR > CRP > > Calciphos > > TPR. The difference found between NCPR and superphosphate is consistent with that reported in the literature for the:;e 2 P sources (Engelstad et al 1974;Chien & Hammond 1978b), as is the difference between SPR and superphosphate (Hammond 1978), CRP and superphosphate (Powell et al 1980;Mackay et al 1980;Rajan 1981b), Calciphos and superphosphate (Buchan et al 1970), and TPR and superphosphate (Hammond & Leon 1977).…”

“…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).…”

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.…”

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.…”