ARTIFICIAL MANURE

Wairarapa Times-Age, 30 September 1942, Page 6

ARTIFICIAL MANURE

PHOSPHATIC FERTILISERS MAIN TYPES. PROPERTIES OF VARIOUS KINDS. In view of the interest being taken in artificial fertiliser by farmers and others, the following explanation of the main types of phosphatic fertilisers will clarify many points at present not generally understood or appreciated, states the Fields Division, Department of Agriculture.. Superphosphate, which is the main phosphatic fertiliser used in the Dominion, is a product manufactured from raw rock phosphate and sulphuric acid. Superphosphate is popular because it is the quickest acting phosphate available and has been demonstrated to be generally useful over the widest range of soil conditions. When applied to the soil, however, a considerable proportion of the phosphate is locked up or virtually lost owing to its combining with certain soil compounds. The possibility of reducing this loss is one which has exercised the minds of both farmer and research worker and consequently the greatest, problem of fertiliser research is how best the ohosphate uptake by the plants may be increased. Despite its general usefulness superphosphate suffers from two other disadvantages, namely, its tendency to set after storage and its destructive effect on bags. Reverted superphosphate or basic superphosate is the name applied to a fertiliser composed of 85 per cent of superphosphate and 15 per cent of lime. Reverted super is not so quick acting as superphosphate. Its lime content has a negligible effect in correcting soil acidity, its chief function being to change the form of phosphate and to correct any excessive acidity in the superphosphate. The addition of life does not increase the ameunt of phosphate in the fertiliser as is sometimes supposed. Apart from the fact that reverted super can be stored without bags being affected, this fertiliser is a safe one to sow in direct contact with any small seeds, as there is no danger of germination damage occurring as is often the case with superphosphate. Serpentine Rock is not a fertiliser in its raw state. At present, its use in agriculture is mainly confined to the preparation of serpentine superphosphate, which is manufactured by the combination of 25 per cent of serpentine rock with 75 per cent of superphosphate. The addition of serpentine rock to superphosphate brings about a chemical reaction producing a completely new product, magnesium phosphate. It is erroneous therefore to view serpentine rock as an adulterant or filler. Magnesium phosphate has been shown by scientific research to be a most effective type of phosphate for plant, use and it is less “fixed” in the soil than is the phosphate in super, that is, a greater proportion remains available for continued plant growth. In the chemical z reaction colloidal silica is also formed and this has been shown to assist in the uptake of phosphate by plants and its presence further increases the efficiency of serpentine superphosphate. The presence of cobalt as a trace element is an added advantage, particularly from a stock health viewpoint. Although the total amount of phosphate in serpentine super per unit weight is less than in super, the lessened quantity is as effective, and is in point of fact, on many New Zealand soils, more effective than is the larger amount of water soluble phosphate in super. Extensive trials conducted over a period of nearly three years have demonstrated that from the chemical and physical viewpoints serpentine superphosphate is superior to ordinary superphosphate. In effect the manufacture of rock phosphate into serpentine super will increase the volume of fertiliser available to the farmer by 33 1-3 per cent —a point of paramount importance at the present time. Serpentine super has in addition to its advantages over super as outlined above, all the good points of reverted super, being free drilling, non-destructive to sacks, and noninjurious to seed, thus making it the most valuable all round type of phosphate to use.