ROTHAMST D RE MANURES.

Otago Witness, Issue 2429, 3 October 1900, Page 4

ROTHAMST D RE MANURES.

In the case of leguminous crops — beans, peas, tares, clovers, etc. — ammonia salts are rarely useful. Mineral^ constituents, especially potash, were applied to red clover -with advantage ; but at Rotliamsted as elseAvhere, good crops of red clover cannot be ensured on arable land unless pome years are allowed to elapse between one crop of that <hy plant and another. In the garden, rowever, which has been filled with plant f .90 constituents by the high cultivation of two or three centuries, xecl clover was sown in 1854, and it has grown luxuriantly in mostof the subsequent years. The famous experiments in wheat-growing in Broadbalk field have attracted as much interest throughout Europe and the United States as in Cheat Britain, and an American agiicultnrisfc knew what he was saying vriien he remarked of them, " Americans have learnt more from this field than from <my c iker agricultural experiments in the world." Tliey have learnt that, after more than 50 years' continuous wheat-growing, Jin unmanured' field -may still, under thorough tillage, yield . an, average of l6f bushels, par acre. .This is 1£ bushels more per acre than the average produce of Australia, Canada, India, the United States, and ten European countries, comprising altogether an acreage ,of over 155,000,000 acres. There could not be a more convincing proof of the inherent capabilities of the soil, and these become more manifest when it is found that a dressing of nitrogen at Rotliamsted doubles the crop of a so-called exhausted field, as it would that of the exporting countries just named. As the mineral constituents of the majority of soils are practically inexhaustible, cheap nitrogen will always mean cheap and abundant corn. In some of the plots where manures are applied, the wheat crops still yield from 40 to 50 bushels per acre, after over 50 years' successive growth of wheat. Next to nitrogen, the most important constituents of plant food are phosphoric acid .and potash, the former being especially useful for roots, the latter for leguminous crops and potatoes. Phosphates have a considerable influence on barley — much greater than in the case of wheat. In the culture of barley the average produce i over 20 years without manure was 20 bushels, and it is a hint worth talcing that the quality of the grain was higher over the second than over the first ten years, so that in attempting to grow the very highest quality of barley on rich soils it will be better it should follow some other corn crop. Farmyard manure gave an average annual yield of 48 bushels per acre ; mineral manures alone gave very poor crops ; nitrogeuous manures alone largely increased the crops, and these with minerals added gave, for 20 years in succession, more grain and straw than did farmyard manure, and considerably more than the average yield of the country under rotation. It may bo laid

down as a general rule, applicable 'to tha heavier class of soils, that barley of good quality may be grr \m with great certaintyafter a corn crop, if the land be gbt into good tilth, and if -401b to 501b of ammonia, salts and 2ewt to 3cwt of mineral superphosphate be applied per acre. These quantities of ammonia would be supplied in l^cwt to> 2cwt sulphate of ammonia, or 1| to 2jcwt of nitrate of soda. The experiments have supplied some valuable facts bearing on the important question of the residual value 0$ manures. In regard to unexhausted manures, it may be noted that when potash or phosphoric acid are applied to crops in excess of their requirements, those substances form insoluble compounds with the soil and become available for future crops. On the contrary, if nitrates or salts of ammonia are not taken up by the crops, they are liable to be washed out by rain and lost, and ifc is owing to the impoverishing effects of excessive rain in washing out fertilising substances from the soil that great- harvests have, seldom followed wet winters. In the removal of heavy crops of wheat, mangel?, etc., which have been grown by the use of nitrates with mineral manures, it is .quite possible that the loss of nitrogen may be made up by. the. amount, stored up" in "the stubble and roots -of these plants. The ?.c.cumulation of -fertility m^ the_ soil^ wfren. dung is continuously applied^ -becomes verygreat. It is not always the most "economical manure, but it is the most bermanenf, and its mechanical effect is favourable. ~Nob a drop ol water has run into the' drains 1a the case of land dressed with dung annually, and such land would naturally sufrer least in time of drought, while it would readily absorb and retain heat and moisture.

The experiments" fliow that a large proportion of the carbon and organic matter of crops is derived from the atmosphere, while the nitrogen raid the mineral matter are taken from the soil. The average annual production has been one ton of grain and straw consisting of 94 or 95 per cent, of atmospheric constituents; or 171b" of potash, 101b of phosphoric acid, and 201b of nitrogen.

Having said so much on nitrogen, wo must not overlook, even in this brief sketch, the discovery of the fixation of free nitrogen by leguminous plants. Chemists had concluded, until recently, that plants had no power of appropriating the nitrogen of the atmosphere, and the discovery that leguminous plant*, have the power of accumulating nitrogen by means of organisms on theii* roots is one of the latest and greatest discoveries of agricultural chemists. The 1 experiments, at Rotliamsted on nitrification, were conducted by Professor Warington, F.Et.S., and it was demonstrated that, by adding to a sterilised sandy soil growing leguminous plants a small quantity of the watery extract of a soil containing the appropriate organisms, a development of the so-called leguminous ncdules on the roots 4<s induced, and ', there is increased growth, and gain of nitrogen. The supposition — now the certainty — .'s that the gain is due to the fixation of nitrogen in the growth of organisms in the root nodules, the nitrogenous compounds so produced being taken, up and utilised by the plant, and, therefore, in the growth of clover, vetches, lucerne, peps, bsans, etc., some of th& nitrogen which they contain, and of the large amount which they leave as nitrogenoxis residue in* the soil, is due to atmospheric nitrogen brought into combination by th& agency of lower organisms. It still remains undetermined how far the failure of clover and other leguminous crops may be due 'to the exhaustion of available combined nitrogen or mineral constituents within tha range of the roots, and how far to the exhaustion of the organisms necessary for bringing about the fixation of free nitrogen^ None of the farm plants, except those bearing a pod, have any power to thus acquire nitrogen. Ie must be obvious, therefore, that it is advantageous to grow' those crops which accumulate fertility rather than. take it out of the land. Every farmer who has grown, clover crops knows that the land appeared richer after that crop, and that little manuring was required for the subsequent crop, and, as a matter of fact, this was not entirely due to the crop heing; fed back by -animals, as where the clover was allowed to go ier seed equally good crops of corn could be grown in the following year. The point was often the subject of discussion until fhe acquirement .of nitrogen otherwise than from' the soil wAs understood, and it was .then -realised thab during the "maturing period of, the plant's -life the greatest benefit was obtained from the nodules, which had then attained their greatest growth. Another instance where farmers of old saw the advantage of growing a leguminous crop was in the case of tares Every farmer knew that on average land he could grow a crop of tares after a, corn crop without applying manure for the leguminous crop ; whereas if in its place h.9 took any other crop, such as wheat, or, in. fact, any other, the plants of which did not make a pod, the yield would be iinsatisfactcry. The reason of the failure of the second crop of cereals would be on account of the deficiency of nitrogen in the soil. But a, crop of tares was found to contain a large amount of nitrogen which the soil cctild not supply. It must therefore have come from some place other than the soil. In fact, like the bulk of any crop, it came from fhe atmosphere, though the bulk of growth was made up not of nitrogen, but the carbon of the atmosphere