FERTILISER TRIALS

Wairarapa Times-Age, 17 January 1941, Page 2

FERTILISER TRIALS

SERPENTINE SUPERPHOSPHATE. DEPOSITS IN NEW ZEALAND. There has been some interest aroused recently in agricultural circles concerning a new fertiliser, silico-super-phosphate, or serpentine superphosphate. as it is also known. Silico-super-phosphate is now manufactured commercially in the Auckland province, in which place field experimental results have justified such a procedure. It is produced at a cost comparable with' that of superphosphate. A similar commercial venture in the South Island is not ye: imminent, however, as field experimentation is far from complete. Ten separate trials with this material are at present being conducted in Western Southland, and the results of these should tell whether silico-super-phosphate will be a successful fertiliser in this district.

Silico-superphosphate is actually a mixture of ordinary superphosphate and serpentine, a mineral which occurs naturally in large deposits in New Zealand, D’Urville Island, in the Marlborough Sounds, harbours a deposit of practically inexhaustible dimensions. Serpentine is one of the silicates, a group of minerals which constitute a considerable portion of the earth’s crust. It is chiefly magnesium silicate, but it also possesses a certain amount of iron, while other elements, notably cobalt arc present in minor quantities. The elements contained in serpentine are considered to be of importance in plant nutrition. "Recent overseas work has shown that silicon is more important in this respect than hitherto thought; magnesium, it is suspected, may be lacking in certain soils in this country: iron is well known as an important soil constituent: and lastly, cobalt has boon shown in the “bush-sick-ness" experiments to be a necessary element in the soil.

It has been found that rock serpentine ground to a suitable fineness and mixed with superphosphate has the effect of reverting the superphosphate, so that most of the phosphate, though not in a water-soluble form, is readily available to the plant. In addition to these chemical aspects of silico-supcr-phosphate, the addition of serpentine to superphosphate lowers moisturecontent. and produces a material less injurious to hags and more pleasant to handle.

At the present time it is officially considered not desirable that any considerable amount of silico-supcrphos-phato be used in the South Island, as this would detrimentally affect the North Island production of fertiliser, and excellent results can be obtained in the South Island by the use of materials such as reverted phosphate, which are readily available to farmers. However, from the experimental point of view the South Island has in no way been overlooked, and at present there are some 37 trials laid down in Canterbury, Otago and Southland which include silico-superphosphate as one of the fertilisers under trial. Six of these trials are on wheat and the balance on grassland. Of the 37 trials, 15 are in Canterbury, seven in Westland 10 in Southland and five in Otago.