Journal of the Royal Agricultural Society of England

as follows: The organisms which fix nitrogen are capable of action only when associated with certain common species of organisms which are capable of oxidising organic matter and which thus surround the anaerobic forms with an atmosphere charged with carbon dioxide and deprived of oxygen. Winogradsky further suggests that the hydrogen set free in the decomposition of the carbohydrates furnishes ammonia, which is assimilated by the micro-organisms and used in the formation of tissue. It is not, therefore, simply the nitrogen which has recently been drawn from the air which is utilised by plants. They assimilate also the nitrogen derived from vegetable and animal remains.

The work of Pasteur has shown that the action of microorganisms is necessary to the transformation of the complex organic substances of the tissues of living plants into the simple forms which may be assimilated by plants. Without these organisms life would be impossible, as Pasteur himself has said, because the work of death would be incomplete. By their intervention the complex substances are burned, the carbon passing into the form of carbon dioxide, the hydrogen into water, and the nitrogen into ammonia; and in these different forms the matter is again carried into circulation.

It often happens that vegetable matter remains for a long time in the form of humus; but even in this form it is utilised by plants. The humus is constantly subjected to the oxidising action of the lower organisms, and undergoes gradual decomposition. The ammonia produced by the decomposition of the humus is assimilated by plants as well as the readily available product of oxidation, nitric acid.

Schloesing and Müntz 20 years ago showed that nitrates are formed in the soil by the action of organisms. More recently Winogradsky has demonstrated that the action of two different organisms is necessary for the transformation of ammonia into nitrates-one converts ammonia into nitrites and the other completes the oxidation, producing nitrates. We thus see that microorganisms seize upon the nitrogen of the air and convert it into organic compounds; they convert vegetable matter into humus, and then break down this humus, producing ammonia and finally nitrates. At every step they perform a useful work, and are valuable auxiliaries of agriculture.

There are, however, other organisms which interfere with the work of the beneficial kinds. Bréal observed several years ago that there is an aerobic organism which decomposes nitrates and sets elementary nitrogen free. This organism is abundant in vegetable débris, especially in straw. It is also encountered in the excrement of domestic animals. The extent to which the losses of nitrogen in arable soils is due to the action of this denitrifying organism and the conditions most favourable to its action are questions which require further investigation.'

See Denitrification and Farmyard Manure. by Professor R. Warington, M.A., F.R.S. Journal R.A.S.E., 3rd series, vol. viii., 1897, p. 577.-ED.

The Different Forms in which Nitrogen is Utilised by Plants.

If we follow the example of Boussingault and plant a sunflower seed in a sterile soil to which the necessary mineral matter and increasing amounts of nitrates are added, or if we repeat the experiment of Hellriegel and plant barley in well-washed sand to which sufficient mineral matter and increasing amounts of calcium nitrate are added, we shall find that the crop produced increases with the amount of nitrate added. In Hellriegel's experiments less than 1 gm. of dry matter was produced when nitrates were not added, the production of dry matter increasing to 25 gm. when sufficient nitrates were supplied.

These experiments, however, simply demonstrated in an exact manner facts which were already well known in practice. The consumption of nitrate of soda would never have reached its present enormous proportions if farmers had not learned to appreciate the efficacy of nitrates as a fertiliser. At the present time they enter into all fertiliser formulas. The application of this fertiliser is necessary, because we are not yet able to so control nitrification in the soil that it can be made to furnish sufficient nitrates for the demands of the crop at exactly the time in the spring when they are most needed. Nitrates are produced only in warm and moist soils, and they are found in the drainage water in larger proportion in autumn than in any other season. Fortunately the roots of living plants have great capacity for retaining the nitrates, and thus reduce the loss in drainage.

If wheat roots are drawn from the soil during the winter, dried, and soaked in sulphate of diphenylamin, they will take on a deep blue colouration. The amount of nitrates contained in wheat roots is surprisingly large. The author has found as much as 1 per cent. in dried roots, but the proportion decreases as growth advances. They pass from the roots to the stems and then to the leaves, where they are used in the formation of albuminoid substances. It might be a matter of surprise that substances which are so easily soluble in water as the nitrates can nevertheless be taken up and retained by roots even when surrounded by moist soil. Demoussy has shown that nitrates can not be removed from the roots by washing in cold water, but are extracted when the roots are treated with warm water or when they are subjected for some time to an atmosphere of chloroform and then washed with cold water. It appears, therefore, that the nitrates penetrate by osmosis into the interior of the cells and form unstable combinations with the protoplasm, resuming their normal state only when the protoplasm is modified by elevation of temperature or the action of chloroform.

Experience has shown that whether nitrates are formed in the soil by the action of micro-organisms, or introduced in the form of fertilisers, they exert a decided influence upon the crop. Nitrates are not formed in soils like those of meadows or forests, which are highly charged with decaying organic matter, since these soils are acid and therefore do not furnish a suitable medium for the nitric ferment. Liming renders such soils more favourable to the activity of the nitric organisms.

In meadow and forest soils nitrogen appears to be taken up by plants in the form of ammonia. Bréal' has shown that nitrogen is also taken up by plants in the form of humates of lime or potash.

Hellriegel has shown in experiments with barley fertilised with variable amounts of nitrates that the amount of water transpired by the plant per gram of dry matter increases as the amount of nitrate applied decreases. Barley, which received the most favourable amount of nitrates, evaporated 260 gm. of water per gram of dry matter produced. The plants which received no nitrates and which made a sickly growth evaporated from 700 to 800 gm. of water per gram of dry matter. Normal, vigorous plants obviously evaporate more water than sickly ones, but if we calculate the ratio of the quantity of water transpired to the weight of dry matter produced we find that the proportion is greater in the sickly than in the vigorous plants. This fact may be useful in determining the efficacy of a fertiliser.

By pursuing this method of investigation the author found that the Gramineæ and Leguminosa do not take up and utilise plant food in the same manner. The Gramineæ are especially benefited by chemical fertilisers, particularly nitrates, while they do not utilise humus substances to very great advantage. On the other hand, Leguminosæ are more benefited by the humates than by nitrates or ammonia salts.

Rye grass and clover were planted in large pots, each of which contained 50 kg. of soil exhausted by continuous cropping. Equal amounts of phosphoric acid, potash, and nitrogen were applied. In one case the nitrogen was applied in the form of nitrates, in the other in the form of humate. A black extract from manure which contained a mixture of humate of potash and humate of ammonia was also used. At the end of the experiment it was found that the rye grass which had received no manure had transpired 682 gm. of water per gram of dry matter, that which had received humates 435 and 469 gm., and that which had received only chemical fertiliser 233 gm. The results were quite different with clover. In this case the transpiration was without manure 454 gm., with chemical fertilisers 398 gm., and with humates 272 and 265 gm. These results confirm the conclusions of Bréal, Snyder, and Lawes and Gilbert. The latter have shown at Rothamsted that it was impossible to grow clover continuously on the same land unless the soil was abundantly supplied with organic manures.

To summarise, then, nitrogen is taken up by plants in the form of nitrates, ammonium salts, and alkaline humates. The Leguminosæ can utilise free nitrogen only when it has been brought into combination by the action of the organisms of the root tubercles. It has frequently been claimed that other plants besides the Leguminosa are capable of absorbing free nitrogen, but it has been shown that this absorption does not take place without the intervention of the organisms which fix nitrogen.

1 Ann. Agron., vol. xx., 1894, p. 353.

VOL. X. T. S.-38.

426

RECENT AGRICULTURAL INVENTIONS.

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