but there are usually nearer 300 lbs. of nitrogen in strong stable manure. It would thus appear that there must be a great loss of nitrogen, and the wheat crop has got the repute, among some writers, of wasting a great deal of nitrogen in its growth.

On another plot of land, where Mr. Lawes raised barley, he applied 200 lbs. of ammonia-salts, which contained 40 lbs. of nitrogen, and raised 40 bushels to the acre. When he doubled his dose, and put on 80 lbs. of nitrogen, his grain was so heavy that it lodged and failed to ripen, and the crop was spoiled. Without the addition of any fertilizer, the soil gave him considerably less than half that amount.

I will mention some other experiments which may give us light on this subject, made by Dr. Hellriegel, who has been studying agricultural problems for some twenty years, having been all this time employed in one of the Experiment Stations kept up in Germany, partly by government and partly by associations of individuals, for the purpose of making agricultural investigations, by the help of chemistry and physiology, and whatever aids can be brought to bear on these questions. Dr. Hellriegel proposed to himself to ascertain what quantities of the different materials which plants require for their growth must be furnished to them in order to get a crop. We have for some years known that phosphates and sulphates of potash, lime and magnesia, and nitrogen must be given, but we need to know how much of each of these various substances is necessary. In order to arrive at accurate results, Dr. Hellriegel had to experiment under artificial conditions. So he took for soil a perfectly pure sand, or one as nearly free from everything that would furnish plant-food as possible. In a large series of experiments, he mixed the soil with a sufficient quantity of all the materials necessary for the support of a crop, with, in each case, one single and different exception. These excepted substances he added in graduated quantities, putting one quantity in one box of soil and a larger in another, and so on through a sub-series of

eight or nine boxes, in order to ascertain by the growth of the plant, in which case he had hit the best proportion of these ingredients. His trials have been extended to the whole list of the elements of the plant. ho found that the growth was tity of this substance with which the crop was supplied. There was a certain quantity of water in the soil necessary to a maximum crop, other things being equal. In the sandy soil which he experimented with, the largest yield of rye, wheat, or oats was obtained when the soil held steadily ten or fifteen per cent of its weight of water. On increasing this proportion, the straw in some cases was heavier, but the grain was reduced in quantity. Thus the very fact that the amount of rain fall is unequal in absolute quantity, and unequal in distribution from year to year, is of itself a reason why you get different crops, everything else remaining perfectly the same. That is a matter always to be taken into consideration in judging of the value or effects of a fertilizer. But it is the effect of nitrogen I am coming at. Dr. Hellriegel experimented with various quantities of nitrogen (in the form of nitrates), applied also to cereals. The plants grew in the artificial soil, consisting of pure sand, with an admixture of ash ingredients in such proportions as previous trials had demonstrated to be appropriate. All the conditions of the experiments were made as nearly alike as possible, except as regards the amount of nitrogen, which, in a series of eight trials, ranged from nothing to eighty-four parts in a million parts of soil. The following table gives the results:*

In regard to water, for example, greatly influenced by the quan

*See also "How Crops Feed," p. 288.

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 uitrogen 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