BASIC SLAG

New Zealand Herald, Volume LXXIII, Issue 22539, 2 October 1936, Page 17

BASIC SLAG

GAINING POPULARITY VALUE OF IMPURITIES FINDINGS OF RESEARCH 11V SUNDOWNER It is; iin acknowledged fact that practice in farming is frequently considerably ahead of scientific research. Thus a great many of the accomplishments of agricultural research workers in the past have had as their chief achievement a discovery of the why and wherefore of the results which practical farmers have secured' from an established practice which is the outcome of trial and error. Biological research, in the true senso of tho word, is an investigation of principles. Later on, when such principles have been established, the scientist can use them as a basis for experimental work, and thus in duo course the farmer reaps the benefit. Ho is then in the position of knowing, for instance, why a certain fertiliser suits a particular soil or gives a better return in grass or crop growth than another which, from the analysis of its main fertilising ingredients, should theoretically give a much better result. Low Phosphoric Acid Content This, perhaps, explains why basic slag, a good samplo of which contains approximately 20 per cent phosphoric acid, 1(3 per cent of which should be soluble in soil acids, is rapidly gaining in popularity in competition with superphosphate, a good sample of which (4-1-1(3 per cent tricalcio phosphate), should contain 20 to 22 per cent of soluble phosphato. Un many heavy soils, especially where the rainfall is high, basic slag gives phenomenal results, both in the quantity and quality of herbago grown. This cannot be satisfactorily explained by its lime content —-lcwt. of basic slag has about the same lime value as lcwt. of calcium carbonate —nor by its phosphatic content, for when these ingredients arc mixed in similar proportions to make a substitute for basic slag, equally good results are not secured. Phosphate More Soluble The higher fertilising value of basic slag may be accounted for by the fact that it is supposed to hold its phosphoric acid, not in the usual form of tricalcic phosphate —as in superphosphate—but in a form known as "tetra-calcic" or "four-lime" phosphate, the chemical nature of which is held to be responsible for the ready availability of the fertilising ingredients of the slag. Basic slag is readily dissolved by any very weak acid, such as a solution of carbon dioxide, hence a much larger proportion of phosphoric acid goes into solution than would be the case with an equally finely-ground sample of tricalcium phosphate containing the sanio amount of phosphoric acid. Recent experiments in Great Britain have proved that the phosphato contained in basic slarr penetrates much more deeply into the soil than does the phosphate in superphosphate. This encourages deeper rooting of the grass and crop plants, since it is a bettor fertiliser to use iu free and open soils and in wet climates which favour deeprooting grasses, or where crops with decp-rooting habits are being grown. Valuable Impurities Another, and very probable, reason why basic slag gives a better response than do many of tho fertilisers with a higher phosphate content is because of its mineral "impurities." Its high limo content definitely tends to improve tha texture ol heavy soils, making them more friable and easier to work. It is also—probably because of its inagesnia, iron and manganese content—a useful preventative of several diseases, the most common of which is "finger-and-toe" in turnips. It has also been shown in recent experiments that the manganese in basic slag, of which there is normal!v ,3 to 5 per cent present, is a definite remedy against "grey speck" disease in oats.

A great many of the North Island soils, and particularly those of volcanic origin where thero is a comparatively heavy rainfall, arc decidedly deficient in available iron and iron compounds. On these soils animal sicknesses, usually referred to as "deficiency" diseases, are liable to occur, and it is on these that basic slag is of the very greatest value. Tho soluble compounds of phosphates, silicates of lime, magnesia, iron and manganese contained in tho slag supply the pasture grass or green crop with these ingredients, and through them tho animals secure their requirements iu an organic form which they can readily assimilate. As a result, stock breed hotter and are much morri healthy on these 'deficient" soils following a liberal top-dressing with basic slag than when depasturing on tho growth resulting from a similar dressing of superphosphate. Further Research Needed

For sonic years past basic slag has been gaining in popularity in New Zealand in spite of the depression and an unfortunate increase in the price of this fertiliser. From results achieved with it on both grass land and crops, farmers are convinced of its superiority—in some districts and climates—to superphosphate. and scientific research is just beginning to toll us why this is so. Tho nature and composition of basic slag is still far from thoroughly understood and its investigation is being steadily continued. Meantime the farmer must be, and is, satisfied with the results which lie gets in tho improved production and health of pastures and stock which ho secures from its use.