LIME AND SLAG

North Canterbury Gazette, Volume 7, Issue 32, 27 August 1937, Page 7

LIME AND SLAG

The Profit Margin INTERVIEW WITH SIR JOHN RUSSELL How much lime or slag is one justified in using? On this question nobody is in a better position to lay down general lines of policy than the Director of Rothamsted Experimental Station, a worldauthority on soil-fertility questions. We quote from the "Farmer and Stock-Breeder”:—

JN these days we hear a great deal about preservation of all sorts of things, not the least being the preservation of ourselves. And so it is in every way fortunate that the Minister of Agriculture is adopting a policy of deliberately preserving the fertility of the soil.

Soil exhaustion is much talked about; the worst consequences are not so much the immediate effects that the loss of soil constituents might have on the crop, as the after-effects on the soil. Loss of organic matter, perhaps the most usual type of soil exhaustion, affects the plant by reducing the supply of nitrogen.

It more profoundly affects the soil, however. You can raise crops perfectly veil by using only artificial manures on a soil that is exhausted of its organic matter, but it is more difficult and more costly; in farming for profit one would not try to do it. Another frequent element lost is calcium, which certainly is a valuable plant food, though the loss rarely goes far enough to amount to actual deficiency. But the after-effects on the soil are very bad, even though there is still enough calcium left for the needs of the plant; for the result of calcium deficiency is to make the soil sour and acid, and of all intolerable things the plant finds sourness or acidity one of the worst. So long as it is there the plant suffers.

Bad Effect Masked The difficulty is intensified by the fact that it is so insidious; some crops do very well; in some years they all do well, and there is nothing to give away the fact that they ought to have done better. The bad effect of acidity is masked by farmyard manure, so that in a year when this is given it may not show itself to any marked extent although it is there all the time. Acidity hardly affects potatoes until it gets really bad; in fact a little acidity is useful because it keeps down potato scab, which otherwise is apt to cause trouble. A potato crop receiving its usual good dressing of farmyard manure would show no harmful effects. But sugar-beet is just the opposite, it is very susceptible to acidity. Many good farmers have lost tonnage on their beet because they failed to realise that their soil was actually acid, thqugh experience with other crops had not shown this lime deficiency. Oats and barley make a similar pair. Oats tolerate some acidity and show no bad effects from it, but barley will not; it fails as soon as a certain acid stage

is reached. Rye and wheat are yet another pair; rye stands up well to acidity while wheat does not. White clover and red clover make a fourth pair. White clover is more tolerant than red, while alsike is more tolerant still.

Swedes, cabbages, kale, and all that tribe (they are all members of the great Brassica family) are in the special position that their commonest pest, the club root organism (which rejoices in the gorgeous name, Plasmc&iophora brassicse) is favoured by acidity while they are not, with the result that acid conditions cause them to become Sadly diseased. Wheat is just the opposite, it is liable to "take-all” on a neutral, soil, but less liable on a slightly acid soil because the "take-all” fungus does not thrive well in acid conditions. In this respect wheat resembles potatoes.

A Sure Sign of Acidity This differential effect gives part of the .explanation of a very curious point about acidity, a little seems to benefit the crop. And so it happens that in an acid field the crops are patchy, the acidity is rarely uniform over the whole field. In places where it is not too strong the crop does well, while in places where it is more pronounced the crop does badly. This patchiness is one of the surest signs of acidity, and the indication becomes certain if on pulling up a plant you find its root is very stunted, if clover is liable to fail, and if mayweed or sorrel comes in. Then lime must be added, but there is no advantage in adding too much. So it happens that the quantity of lime to be added depends not only on the soil but on the cropping system; a rotation based on potatoes, oats, and alsike clover requires less lime than a rotation based on sugar beet, barley, red clover, and rye-grass. It is usually on arable land that lime shows up best, and there are some wonderful successes to its credit. Among the most striking are those at Tunstall in Suffolk where Mr Oldershaw showed that an expenditure of 50/- per acre on chalk resulted in' increased crops worth £64 in the first ten years —surely a big enough return to satisfy anyone. This farm is not peculiar; there are thousands of acres like it.

Grassland does not usually show anything like such a good response to lime. Of course, if the acidity is very pronounced lime must be given, and on some of the Rothamsted grass plots the yield of hay was increased by about 10 cwt. per acre simply by adding lime. On the very acid grass plots at Rothamsted the benefit is very marked, and the limed plots not only yield more but suffered less from winter frost and from spring drought than the unlimed. These plots, however, were already receiving a complete fertiliser. The unmanured plots and those receiving incomplete manures showed no gain from dressings of lime. The plots receiving farmyard manure also showed no benefit, indeed there was some tendency to loss of yield after liming. In an ordinary way the large amount of organic matter in a pasture or meadow soil would mask the usual degree of acidity so that the grass would not need lime.

Grassland and Slag The case alters completely as soon as the grassland is ploughed out, for the protecting conditions then change and the arable land will need lime where the grass did not. What grass land

very often needs is basic slag, partly jierhaps because of a certain amount of exhaustion of phosphate, but partly also because a great deal of the land in grass is naturally short of phosphate, and so failed to give good arable crops and was allowed to tumble down to grass. It is the great merit of the present Government schemes that these two deficiencies are so clearly recognised. In a general way farmers have always known that they ought to use more lime' and more fertiliser, but they simply have been unable to find the money. Now they are to be helped, and they will no doubt respond well to the invitation to improve their land. The steel works are increasing ■ their output of steel, which, of course, means an additional amount of slag. Even more important, the steel makers and the slag grinders have for some years been working together on a Committee appointed by the Ministry of Agriculture and over which I have the honour of presiding, to test the values of different kinds of slag; in consequence, the modern slags are of very good agricultural quality. But although, at the moment, slag is very prominent, it must always be remembered that superphosphate is the most widely used of all the phosphatic fertilisers and that it is good for a wide range of soils and of crops and both for arable and for grassland.

If Potash is Needed The new offers in regard to lime and basic slag are a very good bargain for the farmer but they should not be received in the “bargain basement” spirit as something which you may as well buy now because the chance may never come again. If your soil does not need lime or slag, or if something else would be better, there is no possible point in spending money on them. If the soil is deficient in potash, then potash must be supplied and nothing else will take its place. It used to be thought that lime set potash free from the soil and so did away with the necessity for potash manuring. The Rothamsted grass plots show that that is not so. The plot deficient in potash shows no benefit from lime until the potash is added, and then it does gain. * The yields of hay last year were, in cwt. per acre No Lime Plot lime, added.

7 Complete fertiliser 40.7 51.3 8 Without potash 20.2 17.9

Where superphosphate is known to give better results than basic slag it should be used instead. Every generation of farmers has some special distinction. This generation has learned hoAV to lay, down land to grass. In the old da/s this was not so well understood, indeed, in the old leases it was forbidden to plough out grassland except under penalty because no one could be sure of putting it back again. One of the first things I was taught when I began to study agriculture was “Break a pasture, make a man. Make a pasture, break a man.” When you lay down land to grass, I was told, you may get a decent crop the first year but” ft would almost certainly get poorer and poorer for several years but then gradually if you had luck it might get better. Nowadays this is all changed, and land can be laid down so as to give good results from the start. 'At first there is bare space, but after a comparatively short time a good bottom develops. At Rothamsted we laid down several fields in 1928 and almost from the start they did well while now they are far better than most of the old grass.

The important point is that the management of a pasture is at least as important as the manuring. A farmer who manures his pasture without having the stock to eat down the grass is only asking for trouble.