SOIL FERTILITY.

New Zealand Herald, Volume LXIX, Issue 21141, 26 March 1932, Page 17

SOIL FERTILITY.

EFFECT OF MECHANISATION. ARTIFICIAL AND ANIMAL MANURE A ROTHAMSTED COMPARISON. No. I. At a conference at the Rothamsted Experimental Station in February Sir John Russell, director of tho station, spoke on the effect of mechanisation on soil fertility. Under the old four or five-course rotation, he said, the fertility of 1110. soil was maintained by four different processes, namely:—(l) The straw was converted into farmyard manure; (2) clover was grown once in four years, as far as possible; (3) the roots and the aftermath of clover were fed off on the land by sheep, which received purchased feeding stuffs; (4) artificial fertilisers were given in the root break and sometimes also to the crop. These four methods when properly worked sufficed to keep the land permanently in a good state of fertility. On a four-course rotation por 100 acres of arablo land the annual yield of straw would lie of the order of 80 tons, producing about 300 tons of farmyard manure, and this would give a dressing of 10 tons per acre to the roots, and leave a little over for the " waistcoat of dung which the old farmers like to givo to a piece of backward wheat. The dung, together with the feeding of the roots and tho aftermath on the land, ensured a dressing of animal manure for almost every crop. Supply of Animal Manure. The reduction of the root area, anrl in the amount of sheep feeding on the land, had greatly reduced the amount of animal manure available, and also it had reduced the amount of treading which tho land received. Further, the change in method of feeding animals, whereby more use is made of grass and less of arable land, greatly diminished the amount of farmyard manure available. These tendencies became more and more intensified as mechanisation advanced. It was quite possible to combine a considerable degree of mechanisation with livestock farming, as, indeed, they were doing on tho R-otham-sted farm. Tho problem thus arose: Could fertility bo maintained on an arable farm without- the dressings of animal manure for merlv given ? , . _ " For some years past," said Sir John, " we have been engaged on this subject at Rothnmsted, and a considerable amount of information has now been obtained. We find that the importance of animal manure depends on the kind of crop. " Our experiments on wheat have gone on since 1843, but in recent years they have been extended to deal more fully with this problem. The experiments show that yields of 30 to 40 bushels can be obtained by the use of artificial fertilisers without any organic manure, so long as the cultivation processes keep the land free of weeds. Tho results axe confirmed by the practical experience of John Prout, of Sawbridgeworth, Essex, who, as a profitable commercial venture, grew large acreages of wheat almost continuously from 1861 to 1907 on purely mechanised lines. He occasionally took a red clover crop, but it is not at all clear that this was necessary although it "was probably an advantage. He used no farmyard manure but artificials only and his scheme of manuring was based on the recommendations of Dr. Augustus Voelcker. There was no sign of deterioration of yield. For the first 19 years (18621880) it had been 32 to 36 bushels per acre, and for the 25 years (1880-1904) it averaged 35 bushels per acre, with two loads of straw. Guarantee Against Reduced Yields. " Barley, liko wheat, is independent of farmyard manure and can bo grown quite well with artificials alone. Experience at Rothamsted has, however, brought out ono important result which holds both for wheat and for barley. Farmyard manure steadies the yield, and saves it from dropping so low in bad seasons as it is liable to do when artificials alone are given. This is generally true of all crops and it is one of tho good qualities of farmyard manure not, easily reproducible by artificials. When we come to potatoes and sugar boel. the rase is entirely different. It- is not usually possible to obtain with artificials alone as good yields as when farmyard manure is used. Smaller dressings of farmyard manure can be given when necessary. In that case the dressings of artificials should bo increased, especially the potassic fertiliser. " Mangels come into rather a different category, bo long as yields of only about 25-30 tons per acre are produced, these can be obtained almost as well by artificials supplemented with rape dust or similar organic, as by farmyard manure, and the cropping can be on the same land year after year. Our Barnfield has earned mangels every year since 1876, excepting in two years, 1908 and 1927, when the crop failed owing to bad weather. " Swedes can do without farmyard manure where yields aro 18 tons per acre or less. Where higher yields are possible faimyard manure is required. At Rothamsted our, crops are usually about 15 to 20 tuns per acre. In tho comparisons Available there has been little difference between artificials, when used in sufficient quantity, and farmyard manure."