PHOSPHATE OF LIME.

Auckland Star, Volume LVIII, Issue 41, 18 February 1927, Page 14

PHOSPHATE OF LIME.

THE FOUNDATION-STONE OF

STOCK-REARING.

j A LIMITING FACTOR. I (By PLOUGHSHARE.) It has been estimated that the average expenditure on phosphates is approximately £1 per head of population, men, women and children. Importations came to nearly 160,000 tons last year, to which must be added the very considerable expenditure on grinding, bagging and manufacture. There is every indication that these figures will show a steady increase in the future. So that it is no exaggeration to say that phosphate of lime (the only phosphate in common use) is one of the foundationstones of New Zealand farming: and, further, that in spite of the undoubted fertility of our soil, an increase in exported produce will be accompanied by an increase in imported phosphate. This state of affairs is not very difficult to explain. In the first place, it is now well known that most Xew Zealand soils, especially those of the North Island, are more deficient in phosphate of lime than in any other important plant food. In the second place, the rearing of sheep and cattle is the keynote of New Zealand farming, and phosphate of lime plays a leading part in the formation of bone and sinew. New chemists long ago discovered that certain elements were essential to the life and growth of plants. Field trials very soon demonstrated that, while all fertile soils contained large amounts of all these elements, there were four that were liable to be deficient in that plants readily exhausted such proportion of them as was soluble in soil-acid and therefore available for their use. These four are nitrogen, potash, lime and phosphorus. Nitrogen we seldom run short of in this country, partly because our long hours of sunshine encourage the 1 work of bacteria able to draw on the immense supplies of nitrogen in the air, partly because our soils are for the most part well supplied with humus, which contains appreciable amounts. Potash, too, we have in abundance, though it is not unlikely that in certain cases the supply is running low. But the other two elements, particularly the phosphorus, are notably deficient, so that phosphate of lime is really the limiting factor in our soil economy.

Use Not Exhausting. This point is often overlooked by the farmer, who sometimes has a lurking suspicion that such fertilisers as super are in the nature of artificial stimulants. It is even thought by some that the continued us of phosphatic fertilisers will eventually impoverish the soil, and leave it in a worse condition than when manuring commenced. But when there is so obviously a shortage of phosphate of lime in the 6oil it is surely right to continue to supply it, just as iron is used by doctors to treat anaemic people. When the shortage has been made good, the effect will be indicated by a cessation of the increase in production usually [associated with the use of phosphatic fertilisers, nat by any falling off in production. Then will be the time to look round for other sources of plant food. It appears to make very little differ- [ ence what form the phosphate takes, j This is very fortunate because our sup- [ plies of organic phosphate (bonedust, for example) are distinctly limited and [therefore expensive. From a practical I point of view mineral phosphates are just as effective, so that we can import from the Pacific Islands and other sources the material we need to replace the bone and casein we export in such large quantities. It does, however, appear that water-soluble phosphate (as in super) and citric-acid-soluble phosphate (as in basic super and basic slag) are a j better investment for the farmer than the insoluble phosphate of the untreated rock, at any rate on the average, soil. There is no gainsaying the fact that the 44 per cent of phosphate in super or the 40 per cent in slag generally gives a better financial result than the 88 per cent in the untreated Nauru rock phosphate. In the latter case a large proportion of the insoluble phosphate lies inert in the soil and can only be made use of by plants at a very gradual rate.

Essential to Growth of Stock. The part played by phosphate of lime in the feeding of livestock is well worth studying. Bones, hooves and horns contain very considerable quantities, especially the first-mentioned. There are also appreciable amounts in other parts of the animal body, more particularly the sinews and cartilages. Therefore it is evident that the breeding and rearing of young animals, such as lambs and calves, removes an immense amount of this material.

Milk, again, being designed to build up the framework of the young animal, is rich in phosphate of lime, so that both dairying and lamb-raising (two of our best sources of revenue) are very much more exhausting than the grazing and fattening of stock that have already completed their growth. That is why pastures that graze cows and ewes require a great deal * more top-dressing than those used for the grazing of bullocks and wethers.

It is interesting to note that neither w-00l nor butterfat remove phosphate of lime to any appreciable extent. The latter point is of importance, for, were the dMjt- farmer to redistribute over his arm We skim milk he removes from it through his cows, he could cut down his 5" f f r ti'>sers very considerably. ! n . Practice it pays better to Suf buv X™ to P'" s and <^lves, P?. CeßS *7 P hos P hat . eß from i , " Even when the pigs and mii afi a th extracted the skim Wilitv ; the - v + can .» Jarge amount of s a

What lack of Phosphate Spells,

Lack of phosphate in the soil i s invariably reflected in the stock grazed on it. Young stock become deficient in bone, cows and ewes go off their milk and sooner or later a general unthriftiness sets in. Animals, in their craving for the minerals that the feed cannot supply, take to dewing bones and sticks; this is particularly the case with milking cows, which have not enly

first to form the bones <■( -.\u calf, but subsequently provide iuuugh milk to rear several calves, it is estimated that a cow of moderate milking capacity requires at least 251b of phosphate per annum.

An interesting experiment was recently carried out in South Africa, where lack of phosphates causes a disease known as "styfsiekte," the symptoms of which are both paralysis and rickets. Sixteen heifers were chosen, and grouped as equally as possible in pairs. All were fed a basal ration which contained a minimum of minerals, and the different groups had in addition various minerals in varying quantities. The group fed sodium and chlorine in the form of common salt eventually died of "styfsiekte," as did the group fed commort salt and lime (chalk). The group getting a little phosphate in the form of bone meal developed the ease in a very inild form, while those animals receiving a larger quantity of bone meal were healthy throughout and did well, even when the salt and lime were cut down. In animal economy, as in soil economy, phosphates are by far the commonest limiting factor.

In many countries the practice is now growing of feeding a mineral mixture containing a considerable amount of phosphates. This praetice is sometimes adopted in this country by breeders of highly-productive pedigree stock. For the average farmer, however, there is no doubt that the soundest and most economical way to feed the phosphates on which the health of his stock depends is through his grass and crops.