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ment and which will cause their crops continually to increase and will finally enrich the soil to the extreme limit of its possible fertility.

This would undoubtedly be a vast extension of that admirable humanitarian work for which we are indebted to Pasteur; but this is anticipation, and I only proposed in this lecture to point out the present state of the question. I shall therefore close by summing up what I have said in a few words.

Experiments made by Ville, and repeated and verified by many other observers, have shown us that certain plants, particularly those of the species of the Leguminosa, have taken from the atmosphere a part of the nitrogen that they contain.

Berthelot, and also Gautier and Drouin, have shown that the soil alone can to a slight extent enrich itself by means also of a direct fixation of gaseous nitrogen.

Berthelot has also shown that this phenomenon corresponds with the development of certain microbes preexisting in the soil; and, finally, Hellriegel and Wilfarth have discovered this micro-organism in the nodules on the roots of the Leguminosa.

This last work is certainly one of the greatest interest, and does the greatest honor to the physiologists who have succeeded in bringing it to a final result; but it is proper to recognize that the route to be followed had already been marked out by previous researches. The problem was ripe for solution, and it was in our own countryin France that the great problem of the assimilation of nitrogen had been proposed and in a great part solved, which is no more than was to be expected from so great a center of production and agricultural progress.

Professor Frank, of the agricultural institute in Berlin, finds that the tubercles may be removed from the plant without stopping the process of taking nitrogen from the air. Evidently, therefore, the subject has to be investigated still further. (Agr. Sci., Vol. IV, p. 68.)

Frank has also shown that the symbiosis in the tubercles of the Leguminosa is of an entirely different character from that which occurs in the roots of any other plants. Furthermore, when the soil is rich in humus the microbic parasite does no special service to the host, but when the supply of humus is insufficient the microbe symbiont is of the greatest service to the host. (Agr. Sci., Vol. IV, p. 266.)

H. J. Wheeler, of the Rhode Island Experiment Station, gives (Agr. Sci., Vol. IV, p. 55) an account of the work done by Professor Hellriegel at Bernburg, Germany, along the line of investigation conducted by Boussingault and Ville in France, Lawes and Gilbert in England, and W. O. Atwater, of the Storrs School Agricultural Experiment Station. In the present state of the question it may be considered as settled that certain plants are able, if supplied with all the other essential elements, to draw their supply of nitrogen from

the air, either directly or indirectly, by means of minute organisms now generally termed microbes. These microbes can be communicated by direct inoculation from one plant to another that has been previously free from them. Experiments are in progress as to the possibility of cultivating these microbes artificially, and when this has been accomplished successfully it will mark a great step toward the solution of the question as to. the plant's method of obtaining nitrogen, and not only that, but a great step toward success in agriculture, since every one will be able to inoculate his own plants, and thus immensely stimulate the yield of crops.

T. Leone has shown that a great number of germs obtain their nitrogen more easily by decomposing the nitrates, and only when these salts are used up do they begin to nitrify the ammoniacal compounds, and after that possibly attack the free nitrogen of the air. He has also shown that these take the nitrogen as a gas from the nitric acid in the nitrates and do not convert it into ammonia. Sci., Vol. V, p. 82.)

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Leone also shows that the phenomena of nitrification and denitrification occur alternately according to the relative amount of nutriment and number of bacteria present in the water. The manuring of soil, therefore, gives rise to a cycle of phenomena, nitrification being first arrested and the nitrates and nitrites reduced until a maximum formation of ammonia is attained, when nitrification again commences. The destruction of the nitrates and nitrites in the soil is complete or partial according as the supply of manure is abundant. or otherwise. (Agr. Sci., Vol. V, p. 107.)

The experiments made in Europe by Boussingault, Hellriegel, and others as to the method by which plants obtain the nitrogen from the atmosphere have been repeated and extended by C. D. Woods, of the Storrs School Agricultural Experiment Station. His results are summarized as follows:

(1) Peas, alfalfa, serradella, lupine, probably clover, and apparently all leguminous plants, have the power of acquiring large quantities of nitrogen directly from the air during their growth. There is no doubt that the free nitrogen of the air is thus acquired by these plants. This acquisition has something to do with the tubercles on the roots of these plants, but the details of the process are still to be solved. The cereals, oats, etc., with which experiments have been brought to completion, do not have this power of acquiring nitrogen from the air, nor do they have such tubercles as are formed on the roots of the legumes. They get their nitrogen from the nitrates or nitrogenous fertilizers. The tubercles on the roots of the legumes may be formed either after or entirely without the addition of solutions or infusions containing micro-organisms, and a plausible supposition is that when such infusions are not furnished the spores of the organisms were

floating in the air and were deposited in the pots in which the plants grew. As a rule, the greater the abundance of tubercles the more vigorous were the plants and the greater the gain in nitrogen. The gain of nitrogen from the air by the legumes explains why they act as renovating crops. (Agr. Sci., Vol. IV, p. 22.)

From some careful experiments by A. Petermann on yellow lupins (Lupinus luteus) the author concludes that the physiological rôle of the tubercles must not be exaggerated. They can not be the only cause of the fixation of nitrogen, although their presence may explain why the intervention of atmospheric nitrogen is most marked in the case of the Leguminosa. He further shows that sodium nitrate is not injurious, but beneficial, to lupins. The trouble in its use results mostly from the fact that it is very soluble and is soon washed down by the rain out of the reach of the roots, which must then draw their. nitrogen from the atmosphere by means of the microbic organisms. (Agr. Sci., Vol. IV, p. 264.)

Pagnoul has measured the loss and gain of nitrogen by the soil as the result of the cultivation of special crops. He sowed grass and clover in four pots, but left two others without any crop. The gain of nitrogen permanently fixed in the soil in one year-March, 1888, to March, 1889-was as follows: With no crop the soil gained at the rate of 29 kilograms per hectare per year, with the grass crop 394 kilograms, and with the clover crop 904 kilograms. On the other hand, the total proportion of nitrogen removed from the soil by the drainage water was in each case as follows: No crop, 85; grass, 5; clover, 18. (Agr. Sci., Vol. IV, p. 325.)

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Chapter IX.

RELATIONS OF CROPS TO MANURES, FERTILIZERS, AND

ROTATION.

The preceding section having shown how easily all the valuable nitrates are dissolved and washed away by rain and how completely the permanent fertility of a field depends upon microbic action within the soil, and especially when attached to leguminous plants, we shall therefore not be surprised to learn that expensive and artificial chemical fertilizers and guanos are often less important than the enrichment that comes more naturally by the rotation of crops.

ARTIFICIAL FERTILIZERS AND MANURES.

As the result of twelve years' experience, J. W. Sanborn, of Missouri, states that although both science and practice assert the efficacy of artificial fertilizers, yet their profitable use is a matter of grave concern both in the granite soil of New England and in the richer soil of the Mississippi Valley. His general conclusions are that we do not need to use as much nitrogen in this climate as in Europe, especially as in England, nor as much as has generally been considered necessary; that enriching by rotation of crops is the preferable method; that nitrogen (viz, fertilizers) may be profitably bought only for a few winter or early and narrow-leaved plants, but, as a general truth, broad-leaved plants and those maturing in late summer and in the fall do not require addition of nitrogen to the soil. (Agr. Sci., Vol. I. p. 227.)

From the extensive experiments with fertilizers made at the Ohio Agricultural Experiment Station the following results have been secured, based on both station work and that done by cooperating farmers throughout the State:

Maize. On soils capable of producing 50 bushels of shelled corn to the acre no artificial fertilizer is likely to produce an increase of crop sufficient to pay the cost. On soils deficient in fertility, phosphoric acid may be used with profit.

Wheat. As a rule no more wheat has been harvested from plats treated with commercial fertilizers than from those receiving no fertilizers, whereas farm manures produced a marked increase. At the present prices of grain and fertilizers the increase of crops will not cover the cost of the fertilizer.

Oats. Plats receiving nitrates showed a marked superiority in the growing season, but lodged badly before harvest. Muriate of potash gave an insignificant increase. (Agr. Sci., Vol. IV, p. 237.)

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E. F. Ladd, of the Agriculture Experiment Station at Geneva, N. Y., urges the necessity of a more thorough and systematic study of climate and soil (Agr. Sci., Vol. IV., p. 36) in order that we may better understand the great diversity and contradictions in the experimental field work, so called. Thus one year's experiments at the same station and with all possible care will show that the "Welcome" oats are vastly more productive than the "White Russian," and the very next year reverses this decision. In the same year a neighboring experiment station operating on the same varieties arrives at opposite conclusions. In 1887 the observations showed that fertilizers did not affect the chemical composition of the grasses, but in 1888 the influence was very marked. Ladd finds that the contradictions in the reports of oat crops for 1885 and 1886 at the Ohio and New York stations are apparently due to considering only such factors as monthly rainfall and temperatures. He urges that the soil temperatures, sunshine, wind, the humidity in the soil, and the aeration of the soil are equally important factors. Any season will give some sort of a crop, but the maximum crop must depend upon the fertilizer and the relation of the fertilizer to the season. Thus Warington has shown that a dry and warm season is most favorable for the action of nitrate of soda, while a moderately wet season is most favorable for the action of sulphate of ammonia. The reason of this appears to be that plants are unable to appropriate to their use the sulphate of ammonia until the salt has become nitrified, and this phenomenon of nitrification does not take place except under the influence of a certain amount of moisture in the soil. A soil that conserves its moisture for a considerable time and is properly cultivated to permit the free permeation of the air gives the best results with sulphate of ammonia, but does not necessarily give the best results with the nitrate of soda, since this is so soluble as to be soon drained away out of reach of the plants. Thus in different seasons, with different fertilizers, we have the crops of wheat shown in the following table?

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Again, crops, like animals, have a certain limit to their capabilities; if the maximum yield is 50 bushels per acre, then it is a waste to put on more fertilizer than needed to attain this limit. Evidently, therefore, we have to study the relation of the climate to the fertilizers and the soil in order to ascertain a very important item in the relation between climates and crops.

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