BASIC SLAG.

New Zealand Herald, Volume LXIX, Issue 21146, 1 April 1932, Page 13

BASIC SLAG.

BASIS OF VALUE. PHOSPHATIC EFFECT. ROTHAMSTED EXPERIMENTS. Sir E. .T. liusscll, director of tlio Rotharnsted Experimental Station. in his latest work on artificial fertilisers, deals at length with the experiments with basic slag.

It has been proved that high soluble Slags owe their value chiefly to the soluble phosphorus compounds, but also to the calcium compounds producing the lime effect, and that the low-soluble slags owe their value chiefly to the calcium compounds and to the soluble phosphorus present, or formed by decomposition in the soil. The experiments at Rotharnsted aro in accordance with this view. They show that high-soluble slags produce a phosphatic effect at, once and that lowsoluble slags do not, though they begin to act after a time.

"On grassland that is not too acid or too wet," writes Sir John, "high-soluble slag increases the growth of clover, especially of wild white clover, provided other conditions allow. It may also increase the growth of thistles and of grass. It breaks up the mat of dead vegetation by facilitating decomposition and thus allows rain-water to percolate through the soil more easily. The effect is greatly influenced by the use to which the grass is put.. Engiish Experiments. "Experiments carried out by the Agricultural Education Association at, various centres throughout England and Wales showed that in the first year the highsoluble slag comes out best and, on good land, much the best. In the second and following years the low-soluble slag is improved in effectiveness at the centres where yields were good and in the fourth year the increments were almost as good as those given by the liigh-soluble slag, though the total gain during the foul' years was far less. The mineral phosphate also did better in the fourth year than in the second and third, but, its total effect remained below that of the lowsoluble slag. "The general result is that the highsoluble slag begins to give the return at once and its action continues. The lowsolublo slag and the mineral phosphate take longer to begin. After a time they act fairly well on fome soils, but even at. the end of four years they have not given the same total increase as the highsoluble slag. Effects on Grazing Land.

"Tlio addition of slag to pasture land often results in a striking improvement, especially in the growth of clovcf; so striking, indeed, that in tho early days it was often believed that the slag brought in the clover seeds. It is much more difficult, however, to measure the improvement on grazing land than on hay land. The Cockle Park method of weighing animals at the beginning and at the end of a specified period is admirable for demonstration purposes where tho difference between the slagged and the untreated plots is considerable, but it fails where the differences are smaller, because it can take no account of the selective grazing of tho herbage, or of the grass consumed for maintenance, or of the difference between individual animals. Sheep are used as the grazing animals because they are small and a largo number can be put on to the plots, but unfortunately they cannot cope with grass that has grown more than a few inches high. "Mixed grazing with sheep and cattle keeps the herbage satisfactory, but introduces great difficulties into the experiment, because of the large area of land needed, one bullock requiring about as much land as six sheep. Smaller animals than sheep might be used. For example, one sheep is equivalent to about three geese. A simpler method is to leave tho plots unfenced and accessible to all the animals and then closely to watch the herbage and the choice exercised by the animals. This gives information as to palatabilitv and is useful in tho hands of a competent*, unbiased observer using ecological methods of herbage analysis.

"A third method is to fence in the grass, thus protecting it from the animals. Lut to cut it frequently by a mowing machine, and to weigh and analyse the cuttings. This method has the advantage of giving quantitative results, but the disadvantage that mowing is not quite the same as grazing. None of these methods is as accurate or as trustworthy as those used for hay or for arable crops. Attempts are being mado at liothamsted to improve the grazing method and to givo it quantitative significance. Results on Olay Land.

"hoanis on which grass and clover already grow well may show little response. Much depends on the efficiency of the grazing. If the grass is kept closely eaten down, by cattle and sheep grazing together, slag may increase the yield of meat or milk, but if ifc is allowed to grow and is grazed by sheep only, it. may pass beyond the stage at which the animals thrive upon it. Unlesj the grazing is adequately done, slag may do nioro harm than good on. this typo of land.

"Clay land usually responds to slag better than does any other. The most spectacular improvement is on wet, sour clay land, only sparsely populated with vegetation, so that there is much unoccupied surface—in particular land that is carrying little or no clover, but a relatively large amount of bent grass, which dies and goes brown in the autumn. Such is the land of Cockle Park and much of the Boulder clay of the Midlands of England. Addition of slag causes a remarkable spread of clover, usually the wild wliito variety (Trifolium rcpens), which rapidly colonises the unoccupied land and which, by enriching tho soil in nitrogen and in humus, favours the development, of useful grasses. The impiovement is striking; it is at least as good as can be obtained by cake-feeding and is much cheaper. On very acid soils or very wet soils, a mat oi dead vegetation is apt to form and render colonisation by clover impossible. Slag cannot then act until the excess of water is lemoved, the acidity neutralised and the mat destroyed so that tho bare earth is exposed."