INCREASED FERTILITY

Wanganui Chronicle, Volume 77, Issue 154, 2 July 1934, Page 9

INCREASED FERTILITY

USE OF SUPERPHOSPHATE EXTENDED TIME OF EFFECT DECREASED SOIL ACIDITY Despite the fact that superphos phate is by far the most popular fer liliser used throughout New Zealand there are still some fanners who wil not use it because they have been told First, that it is only a short-livee stimulant, and secondly that it is ar acid fertiliser and as such is likely t< increase soil acidity. No evidence ii support of these mistaken ideas i: ever brought forward, ior the simple reason that no such evidence is avail able. If there was the least suspicioi that super was merely a ilash-in-the pan” in so far as increasing crop oi pasture production is concerned, 01 that its continued use would increase soil acidity, surely such suspicions would have been confirmed during th< 90 years that superphosphate has beei in use. As a matter of fact, the evi dence is all the other way, and super phosphate owes its popularity to th* combined facts that it is the ruosi active of all phosphatic fertilisers that it is decisive in its action, that it is lasting in its effect, that it ro duces soil acidity, that it is safe tc use for all crops and that it is always in good drilling condition. With a wide range of phosphatic fertilisers tc choose from, the farmers of thi> Dominion have decided almost unani mon sly in favour of superphosphate, and in doing so they have confirmee not only their own practical results but the experimental results of scien tists and research workers in every country of the world. Those men whe continue to hold to the belief that there are better forms of phosphate *1 their disposal have only to look at the figures published in London by the International Manufacturers’ Association covering the world s consumption of phosphoric acid for agricultural purposes. The figures read:— Tons As superphosphate 15,050,000 In all other forms 6,000,000 When it is realised that this return covers countries where the standard

grade of superphosphate is a low one compared with ours, and where other forms of phosphate are relatively cheap, the figures quoted here assume added importance. Bothainsted Reports Referring back to the suggestion that superphosphate has no staying powers, it is interesting to read what the director of the Rothamsted Experimental Station in England has to say about it. In his annual report for 1933 Director Sir E. J. Russell says: —“The fact that superphosphate does not wash out from the soil obviates the necessity for applying it to every crop; it can be given once or twice m a rotation and some not taken up by one crop remains available for succeeding crops.’’ In the same publication we read that a crop of swedes to which a dressing of superphosphate was applied yielded only a few tons per acre better than a crop grown on iand to which superphosphate had been applied one year before the swedes were sown. It is a fact that superphosphate acts quickly and it may be that quick action which deceives one at times. We are apt to expect in the second month the same phenomenal results as are usually apparent the first month after applying a dressing of superphosphate, whereas by that time the phosphoric acid contained in the superphosphate has become slower in action through its combining with the lime in the soil. In spite of this slower action, however, the super is still maintaining the increased growth noticed earlier, and in addition is permanently building up the phosphate and calcium contents of the crop. Super does not merely increase yield per acre, but it definitely improves the quality of the crop to which it is applied. An important effect from the use of superphosphate is the greatly-increased weight of the roots of plants in a pasture or crop. Some interesting results from the U.S.A, show that a dressing of superphosphate just doubled the weight of the root system of a crop of maize; individual plants showing a dry matter weight of 43.7 grammes for “no manure,” compared with 88.5 grammes for “treated with super. ” Perhaps this effect of superphosphate on the root system explains, at least in part, how Mr. R. B. Tennent, whilst in charge of the Otago and Southland districts as fields superintendent, was able to record increases in hay yield for three seasons following a light topdressing with super. The records referred to appear in the New Zealand Journal of Agriculture for May, 1932, and concern some simple trials carried out in various parts of Otago. Ono set of trials showed that, compared M'ith “no manure,” super gave an increase of 68 per cent, in the first year, 12 per cent, in the second and 9 per cent, in the third year after application. Results such as these do not support the contention that super is a short-lived stimulant. The Acidity Question Superphosphate is still frequently ipoken of as being an acid manure, no doubt this being due to the fact that sulphuric acid is used in its manufacture. To suggest, however, that prop-erly-matured super contains any free sulphuric acid is doing this popular fertiliser a grave injustice; no one conversant with the process of manufacture could ever be guilty of making such an accusation against super. It is true that super does contain a trace of free acid, but that acid is phosphoric acid, or, in other words, the plant food for which super is so famed. Ag soon as the super comes into contact with the soil the phosphoric acid, both free and combined with calcium, is available to plants and the residue left in the soil is gypsum or sulphate of lime—a substance that actually has power to reduce acidity. Tn superphosphate the acid is the plant food and th e residue a neutralising agent, whereas in a correctly-described “acid manure” the plant food is neutral and the residue is acid—a complete reversal of the “super” position. Rothamsted Opinions Sir E. J. Russell refers to this question of superphosphate and soil acidity when he states: “The old statement that superphosphate tended to exhaust the lime and to make the soil acid is incorrect. The continuous experiments at Woburn provide an excellent oppor-

tunity ior testing the effects of superphate on the reaction of the soil. Although sulphate of ammonia made the soil so acid that the barley and wheat failed completely in about 20 years, superphosphate with potassium ~ sulphate had no such effect, but actually i educed the acidity and increased the exchangeable calcium in the surface soil.” On both light and heavy soils the effect of continuous applications of superphosphate has been to decrease soil acidity, especially in the tc-p 6in. of soil. At Woburn no less than 81 tons of superphosphate per acre had been applied in regular dressings between 1856 and 1924, the total quantity used per acre was 12 tons, yet in each case the soil was less acid at the finish than it was at the start. Here in New Zealand we have scientific evidence in support of the statement that superphosphate does not increase soil acidity. At Marton Experimental Area, Mr. Hudson has found that repeated dressings of super have definitely lowered the soil acidity. There is a mass of evidence winch places beyond doubt the claim that superphosphate ctrq and does reduce soil acidity and * pitted against this mass G’f accurately-measured research, the loosely-worded statement i|ri superphosphate increases acidity seems a pitiable affair.