Good D.D.T. Superphosphate Mixes Now Possible

Press, Volume XCVIII, Issue 28980, 22 August 1959, Page 9

Good D.D.T. Superphosphate Mixes Now Possible

'P'ROM time to time criticism has * been heard of D.D.T. superphosphate mixes made by fertiliser works. Happily recently at the Massey College sheepfarmers’ conference Mr J, M. Kelsey, officer in charge of the entomological sub-station of the Entomology Division of the Department of Scientific and Industrial Research, was able to give a very favourable report on the latest analyses of commercial mixes. Of interest to Canterbury farmers will be an account of the mixing procedure followed at the Hornby works of Kempthorne, Prosser and Company and the difficulties involved in mixing super and D.D.T. which has been prepared by Mr D. H. Murdoch, the works manager. “The introduction of D.D.T. fertilisers on a large scale began in Canterbury in 1952 and it was soon realised that the mixing of two such physically dissimilar materials as D.D.T. powder and superphosphate presented special problems and that existing mixing methods would not be satisfactory,” says Mr Murdoch. “Accordingly, a D.D.T. mixing plant was designed and erected at Kempthorne, Prosser and Company’s Hornby works. In the machine the mature superphosphate or other fertiliser Is first screened to remove lumps or foreign material and then enters a skip hoist in batches of two tons. To the fertiliser in the skip is added from a sealed drum a weighed quantity of powdered D.D.T. containing the requisite equivalent of the para para isomer. The skip is then elevated to a height of 38 feet and the charge deposited into a double cone mixer nine feet in length and seven feet in diameter. The mixer which contains internal flights to facilitate mixing is then rotated for five minutes or 110 inversions. The mixture is then discharged into a hopper, automatically weighed into bags, the

bags closed by a sewing machine, and conveyed to the waiting vehicle.

“In spite of the apparent simplicity of the process a number of difficulties arise in practice, mainly in connexion with the variable physical properties of D.D.T. powder. The earliest D.D.T. powders u'sed were rather low in grade and hence contained a considerable proportion of filler. They were free flowing and produced excellent mixtures with superphosphate. “In 1958 the World Health Organisation, which is the largest consumer of D.D.T., changed its specifications for powdered D.D.T. and for some time this was the only material available. This powder contained much less filler and the inherent waxy nature of D.D.T. was not suppressed to the same extent as formerly. As a result, the powder showed a tendency to agglomerate into tiny balls and was difficult to incorporate into superphosphate. More recently some manufacturers have again begun to produce D.D.T. powder containing more filler and these products show outstanding mixing properties and will be used in future. As additional filler reduces the p.p.i. contents, more D.D.T. is, of course, added to mixtures to arrive at the correct quantity specified by the D.5.1.R., i.e., 21b 100 per cent, p.p.i. per acre. “All shipments of D.D.T. powder are analysed for para para isomer content and are microscopically sized for average particle diameter.

“Due to the introduction of these newer grades of D.D.T. powder and to modifications in the mixing technique, D.D.T. fertilisers can now be produced in which there is no agglomeration of D.D.T. or variations in D.D.T. content from bag to bag within the limits of uniformity of plus or minus 2J per cent.”