Effect of various Proportions of Assimilable Nitrogen in the Soil.

The maximum crops of wheat and rye were obtained with eighty-four parts of nitrogen to one million parts of this soil, but the maximum oat crop was got with fifty-six parts of nitrogen, at least; the gain between fifty-six and eighty-four parts of nitrogen, in the case of oats, was a mere trifle. Dr. Hellriegel made some other observations, which he has not reported in detail, which led him to conclude that he might have got his best crop of wheat with seventy parts of nitrogen, his best crop of rye with sixty-three parts, and his best crop of oats with fifty-six parts, to a million parts of soil. This soil which he used was not a large absorbent or fixer of the substances furnished to the plant. The nitrogen which he used was in the form of nitrates, which are never absorbed by soils, so far as we know. The matters with which he enriched the sand, therefore, were soluble and entirely available to the plant. The latter had only to stretch out its roots to obtain its food, and the quantity of soil was small, so that the roots had not far to travel, and could so completely occupy the soil as to come in contact with all the nourishment it contained. QUESTION. Does nitrogen form a part of the plant? PROF. JOHNSON. Yes; an important part, always. QUESTION. How large a part?

PROF. JOHNSON. In the entire plant, when dry, from onehalf to two per cent. In the different parts of plants it varies greatly. You have fifteen per cent. of nitrogen, for example, in the gluten of wheat; one and one-half to two per cent in

the wheat grain; you have no nitrogen whatever in pure cotton fiber; there is no nitrogen in the sugar or in the starch of the plant.

QUESTION. Does it exist in the wood in the form of nitrate? PROF. JOHNSON. No; but in the form of what is called albuminoids; something which is similar to the albumen or white of the eggs of animals.*

MR. S. L. GOODALE, of Saco, Maine. What is the comparative value of a given amount of nitrogen, in ammonia salts and in animal substances, such as blood, flesh, dung?

PROF. JOHNSON. It is very difficult to say; but these experiments of Mr. Lawes show that in order to get thirty-six bushels of wheat to the acre, he used two hundred pounds of nitrogen, in the form of stable manure, whereas eighty pounds of nitrogen used in the shape of salts of ammonia, gave the same crop. The reason of that is that the nitrogen of the salts of ammonia is in a condition to be made immediately available to the plant, whereas the nitrogen in animal manure exists in a form or in forms such that much of it cannot be taken up by the plant at once, if at all. It must undergo an alteration to become of use, and much of it, instead of passing into an available condition, doubtless becomes permanently inert.

MR. S. L. GOODALE, of Saco, Maine. What are the circumstances under which the nitrogen of manure is converted into into ammonia, which is retained in the soil, and what the circumstances in which it is converted into nitrates, which may pass out of the soil?

PROF. JOHNSON. So far as can be judged from our imperfect knowledge, a rapid decay of nitrogenous matter which goes on with comparative exclusion of air, generates ammonia; on the other hand, where there is a large access of air, there we have nitrates formed. But we do not know minutely the conditions under which nitrates are produced. Another fact to be noticed is this: that in the decay of animal matters with

*See "How Crops Grow," pages 94 to 109.

access of air, there is invariably a quantity, and often a large quantity, of nitrogen liberated in the state of free, gaseous nitrogen, such as exists in the air about us, and which does not assume the form either of ammonia or nitrates, and thus becomes lost as a fertilizer.

MR. GOULD. Before the current of questions drifts away from the main subject of the lecture, I am desirous of asking the Professor a question as matter of explanation. He has stated a distinction among plants-plants which exhaust the nitrogen and plants which accumulate nitrogen, in the soil. This is a subject of immense practical importance, and I think it will play a much greater part in questions of practical farming, than it ever has done in the past. The statement which he made would justify the inference, although he did not state it himself, that plants accumulate nitrogen in the soil in proportion to the surface of their foliage extended to the air, and to the length of time during which that foliage is in actual growth. The inference would be that there was a proportion between the amount of accumulation and the length of time. I desire to know whether the Professor wishes to be understood in that way?

PROF. JOHNSON. I would not assert that to be the fact, absolutely or unqualifiedly, but the indications very strongly favor that general conclusion.

MR. GOULD. That is my own personal impression. I wished to know whether the Professor so understood it.

PROF. JOHNSON. I was about to say how much nitrogen was needed in the soil.

A wheat crop of thirty-three bushels, with straw and chaff, contains fifty-six pounds of nitrogen. If we allow for stubble and roots one-fifth this quantity, we have for the total nitrogen required in the vegetation of an acre of wheat, say sixty-eight pounds.* Hellbriegel found, by actual trial, seventy pounds

*On examination of wheat roots collected by Schubart June 8th, 1855, Stockhardt found that the roots composed a little more than one-fifth of the entire plaut, or

of nitrogen to be sufficient to produce his maximum wheat crop.

: Mr. Lawes' soil furnished enough nitrogen to yield seventeen bushels of wheat. Addition of forty-one pounds of nitrogen, in form of ammonia salts, gave twenty-seven bushels, or an increase of ten bushels. Eighty-two pounds of nitrogen applied in the same form gave thirty-seven bushels, or twenty bushels increase.

The reason why Mr. Lawes was obliged to add eighty-two pounds of nitrogen to double the wheat crop, lies in the following considerations:

When ammonia is applied as manure, a portion of it is fixed in a comparatively insoluble condition in a clayey or loamy soil, and a share of this fixed ammonia it is doubtless very difficult for the plant to acquire. Again, nitrification, or conversion of ammonia into nitrates, goes on, and the nitrates are freely soluble and wash out of the soil. Then we know that the roots of the plant cannot come into contact with the whole of the soil, so that we should not expect that all the available nitrogen there would be taken up. The figures show that from seventy to eighty pounds is sufficient, provided it iş in a form and in a position in which the plant can appropriate it. In stable manure we appear to waste a considerable quantity simply because it is not present in a form in which the plant can use it.

Now, stable manure, when it is put into the soil, may be compared with clover roots or any other vegetable matter put into the soil. Stable manure consists very largely of vegetable matter which has passed through animals, and of more or less litter which we mix with it. There is a small portion of the

twenty-two per cent, and the nitrogen of the roots was a little less than one-fifth that of the entire plant, or eighteen per cent.

Heiden found the nitrogen of the roots of ripe rye but one-tenth that of the entire nitrogen. Stockhardt's examination was made on the unripe wheat. By ripening, the proportion would doubtless have been reduced. Heiden found, in fact, that the ratio of root to top in blossoming rye was about one to six, but in ripening was reduced to one to thirteen and one-half.

If, then, the roots alone contain one-tenth of the entire nitrogen, the roots and stubble may be fairly reckoned to contain one-fifth of the entire nitrogen.

Weiske, indeed, gives twenty-two pounds of nitrogen per acre for the roots and stubble of wheat, but we are not informed how high the stubble was cut.

nitrogen of the manure actually formed into these ammonia salts which Mr. Lawes applied, but most, of the nitrogen, in order to to be used by the plant, must be transformed, must pass into some other state than that in which it exists in the manure itself; must probably either be converted into ammonia or nitrates.

MR. LYMAN. Suppose the case that I wish to use all the liquids of my stock, and absorb it all, and do not pay so much attention to the coarser manure. What, in your judgment, is the relative value of the one placed by the side of the other? This question is being agitated extensively.

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PROF. JOHNSON. That depends somewhat upon the food which the animals have. If they are kept upon low rations the liquids would be the best. But if they are supplied with rich food, grain, meal or oil-cake, that indeed increases the value of the liquids, but increases more, relatively, the value of the solids, because you cannot get into the circulation of the animal beyond a certain amount of nutritive matter; but you can run through the intestinal canal much more material which is only partially digested, and so the value of the solid manures, as compared with the liquids, is increased by increasing the richness of the food.

When oxen or other herbivorous animals are kept on rations which just maintain them without much gain or loss of live weight, the daily urine usually contains rather more nitrogen than the dung. Sometimes the nitrogen of the dung exceeds that of the urine, but while all the nitrogen of the urine is adapted for immediate use as plant food, much of that in the dung is comparatively inert. The urine contains also more alkalies than the dung, but the dung usually contains all the phosphoric acid and most of the lime.

Measured by assimilable nitrogen or by alkalies, the liquids are much the best; measured by phosphates, the dung is most valuable. Practically, however, we cannot make a sharp separation. The solids nearly always absorb a good portion of the liquids.