The nitrogen of the atmosphere is not called into requisition, except by a few plants and under special conditions, as will be explained later.
Manures), manufactured or imported, to state the percentage of the nitrogen, of the soluble and insoluble phosphates, and of the potash in each article sold, and this statement was to have the effect of a warranty.
The power of fixing atmospheric nitrogen by the higher plants seems to be confined to this solitary group, though it has been stated by various observers with more or less emphasis that it is shared by others.
Similar observations have been made in the case of various compounds of nitrogen, though these have not been so complex as the proteids.
Indicates that if 28 grammes of nitrogen could be made to unite directly with 16 grammes of oxygen to form nitrous oxide, the union would cause the absorption of 18500 calories.
The exhaustion of the soil induced by both barley and wheat is, however, characteristically that of available nitrogen; and when, under the ordinary conditions of manuring and cropping, artificial manure is still required, nitrogenous manures are, as a rule, necessary for both crops, and, for the spring-sown barley, superphosphate also.
Since Hellriegel's striking discovery farm crops have been conveniently classified as nitrogen-accumulating and nitrogenconsuming.
These are: (I) That the green plant is so stimulated by the symbiotic association which leads to the hypertrophy, that it is able to fix the nitrogen or cause it to enter into combination.
It was in the year 1886 that Hellriegel and Wilfarth first published in Germany the results of investigations in which they demonstrated that, through the agency of micro-organisms dwelling in nodular outgrowths on the roots of ordinary leguminous plants, the latter are enabled to assimilate the free nitrogen of the air.
Under this system the clover is ploughed up in the autumn, the nitrogen stored up in its roots being left in the soil for the nourishment of the cereal crop. The following summer the wheat crop is harvested, and an opportunity is afforded for extirpating weeds which in the three previous years have received little check.
The root-crops, indeed, may contain two or more times as much nitrogen as either of the cereals, and the leguminous crops, especially the clover, much more than the root-crops.
Whichever opinion is held on this point, there seems no room for doubt that the fixation of the nitrogen is concerned only with the root, and that the green leavec take no part in it.
The attitude taken up later on with regard to this problem is set forth in the following words, which are quoted from the Memoranda of the Rothamsted Experiments, 1900 (p. 7): - " Experiments were commenced in 1857, and conducted for several years in succession, to determine whether plants assimilate free or uncombined nitrogen, and also various collateral points.
The greater part of the nitrogen of the cereals is, however, sold off the farm; but perhaps not more than to or 15% of that of either the root-crop or the clover (or other forage leguminous crop) is sold off in animal increase or in milk.
Most of the nitrogen in the straw of the cereals, and a very large proportion of that of the much more highly nitrogenyielding crops, returns to the land as manure, for the benefit of future cereals and other crops.
Wouldn't that be something: Plants that would convert nitrogen from the atmosphere directly into ammonia they could use or plants that gave off the odor of other plants that pests avoid?
It is certain that their protoplasm cannot be nourished by inorganic compounds of nitrogen, any more than that of animals.
The fate of these inorganiccompounds has not been certainly traced, but they give rise later on to the presence in the plant of various amino acid amides, such as leucin, glycin, asparagin, &c. That these are stages on the way to proteids has been inferred from the fact that when proteids are split up by various means, and especially by the digestive secretions, these nitrogen-containing acids are among the products which result.
Up to very recently the original absorption and subsequent treatment of the carbon dioxide and the compounds of nitrogen has been called by the same term.
Long ago the view that this gas might be the source of the combined nitrogen found in different forms within the plant, was critically examined, particularly by Boussingault, and later by Lawes and Gilbert and by Pugh, and it was ascertained to be erroneous, the plants only taking nitrogen into their substance when it is presented to their roots in the form of nitrates of various metals, or compounds of ammonia.
The chamber has a safety value at the top of its vault, which is so balanced that the least surplus pressure from within sends it up. The first puff of sulphur vapour which enters the chamber takes fire and converts the air of the chamber into a mixture of nitrogen and sulphur dioxide.
To the former belong the ordinary leguminous crops - the clovers, beans, peas, vetches or tares, sainfoin, lucerne, for example - which obtain their nitrogen from the air, and are independent of the application of nitrogenous manures, whilst in their roots they accumulate a store of nitrogen which will ultimately become available for future crops of other kinds.
It is, in fact, fully established that these leguminous crops acquire a considerable amount of nitrogen by the fixation of the free nitrogen of the atmosphere under the influence of the symbiotic growth of their root-nodule-microbes and the higher plant.
In Canada and the United States this rational employment of a leguminous crop for ploughing in green is largely resorted to for the amelioration of worn-out wheat lands and other soils, the condition of which has been lowered to an unremunerative level by the repeated growth year after year of a cereal crop. The well-known paper of Lawes, Gilbert and Pugh (1861), " On the Sources of the Nitrogen of Vegetation,.
With special reference to the Question whether Plants assimilate free or uncombined Nitrogen," answered the question referred to in the negative.
As to the source of the nitrogen of the root-crops-the so-called " restorative crops "-these are as dependent as any crop that is grown on available nitrogen within the soil, which is generally supplied by the direct appli cation of nitrogenous manures, natural or artificial.
Under such conditions of supply, however, the root-crops, gross feeders as they are, and distributing a very large extent of fibrous feeding root within the soil, avail themselves of a much larger quantity of the nitrogen supplied than the cereal crops would do in similar circumstances.
When a full supply of both mineral constituents and nitrogen is at command, these root-crops assimilate a very large amount of Table Xi.-The Weight and Average Composition of Ordinary Crops, in lb.
The still more highly nitrogenous leguminous crops, although not characteristically benefited by nitrogenous manures, nevertheless contribute much more nitrogen to the total produce of the rotation than any of the other crops comprised in it.
It is the leguminous fodder crops-especially clover, which has a much more extended period of growth, and much wider range of collection within the soil and subsoil, than any of the other crops of the rotation-that yield in their produce the largest amount of nitrogen per acre.
The nitric acid is most likely taken up chiefly as nitrate of lime, but probably as nitrate of potash also, and it is significant that the high nitrogen-yielding clover takes up, or at least retains, very little soda.
Sea Island cotton seed is rather more valuable than Upland: the corresponding figures for the three principal constituents being nitrogen 3.51, phosphoric acid 1 69, potash 1.59%.
Heating spirits of hartshorn, he was able to collect "alkaline air" (gaseous ammonia), again because he was using mercury in his pneumatic trough; then, trying what would happen if he passed electric sparks through the gas, he decomposed it into nitrogen and hydrogen, and "having a notion" that mixed with hydrochloric acid gas it would produce a "neutral air," perhaps much the same as common air, he synthesized sal ammoniac. Dephlogisticated air (oxygen) he prepared in August 1774 by heating red oxide of mercury with a burning-glass, and he found that in it a candle burnt with a remarkably vigorous flame and mice lived well.
But it gave some impetus to the practice of green manuring with leguminous crops, which are equally capable with such a crop as mustard of enriching the soil in humus, whilst in addition they bring into the soil from the atmosphere a quantity of nitrogen available for the use of subsequent crops of any kind.
Moreover, the crops alternated with the cereals accumulate very much more of mineral constituents and of nitrogen in their produce than do the cereals themselves.
Of the nitrogenous compounds in food, on the other hand, only a small proportion of the whole consumed is finally stored up in the increase of the animal - in other words, a very large amount of nitrogen passes through the body beyond that which is finally retained in the increase, and so remains for manure.
As, however, the manure of the animals of the farm is valuable largely in proportion to the nitrogen it contains, there is, so far, an advantage in giving a food somewhat rich in nitrogen, provided it is in other respects a good one, and, weight for weight, not much more costly.
If not, there must exist in the green plant, side by side with it, another mechanism which is concerned with the manufacture of the complex compounds in which nitrogen is present.
Fixation of Nitrogen.Another, and perhaps an even more important, instance of symbiotic association has come to the front during the same period, it is an alliance between the plants of the Natural Order Leguminosae and certain bacterium-like forms which find a home within the tissues of their roots.
While they are quite capable of taking up nitrates from the soil where and so long as these are present, they can grow and thrive in soil which contains no combined nitrogen at all, deriving their supplies of this element in these cases from the air.
The exact way in which the utilization or fixation of the nitrogen is effected remains undecided.
Trans., 18 53, p. 357, 18 54, p. 321, and 1862, p. 579) showed that the statement that no internal work is done when a gas expands or contracts is not quite true, but the amount is very small in the cases of those gases which, like oxygen, hydrogen and nitrogen, can only be liquefied by intense cold and pressure.