Talks on Manures Part 57

An inspection of the property brought out the following facts--that all the land was very light, and that you might walk over the fresh plowed surface in the wettest weather without any clay sticking to your boots: still a portion of the soil was dark in color, and therefore probably contained a sufficient amount of fertility to make cultivation profitable, provided the management could be conducted with that care and economy which are absolute essentials in a business where the expenditure is always pressing closely upon the income.

Upon land of this description meat-making is the backbone of the system, which must be adopted, and a large breeding flock of sheep the first essential towards success.

Science can make very little improvement upon the four-course rotation--roots, barley, clover, and wheat, unless, perhaps, it may be by keeping the land in clover, or mixed gra.s.s and clover, for two or three years.

A good deal of the land I was inspecting was so light, that, in fact, it was hardly more than sand, and for some years it had been left to grow anything that came up, undisturbed by the plow.

To a practised eye, the character of the natural vegetation is a sure indication of the fertility of the soil. Where herds of buffaloes are to be seen--their sides shaking with fat--it is quite evident that the pastures upon which they feed cannot be very bad; and in the same way, where a rank growth of weeds is found springing up upon land that has been abandoned, it may be taken for certain that the elements of food exist in the soil. This ground was covered with vegetation, but of the most impoverished description, even the "Quack" or "Couch-gra.s.s" could not form a regular carpet, but grew in small, detached bunches; everything, in fact, bore evidence of poverty.

Possibly, the first idea which might occur to any one, on seeing land in this state, might be: Why not grow the crops by the aid of artificial manures?

Let us look at the question from two points of view: first, in regard to the cost of the ingredients; and, secondly, in regard to the growth of the crop.

We will begin with wheat. A crop of wheat, machine-reaped, contains, as carted to the stack, about six pounds of soil ingredients in every one hundred pounds; that is to say, each five pounds of mineral matter, and rather less than one pound of nitrogen, which the plant takes from the soil, will enable it to obtain ninety-four pounds of other substances from the atmosphere. To grow a crop of twenty bushels of grain and two thousand pounds of straw, would require one hundred and sixty pounds of minerals, and about thirty-two pounds of nitrogen; of the one hundred and sixty pounds of minerals, one-half would be silica, of which the soil possesses already more than enough; the remainder, consisting of about eighty pounds of potash and phosphate, could be furnished for from three to four dollars, and the thirty-two pounds of nitrogen could be purchased in nitrate of soda for six or eight dollars. The actual cost of the ingredients, therefore, in the crop of twenty bushels of wheat, would be about ten to twelve dollars. But as this manure would furnish the ingredients for the growth of both straw and grain, and it is customary to return the straw to the land, after the first crop, fully one-third of the cost of the manure might, in consequence, be deducted, which would make the ingredients of the twenty bushels amount to six dollars. Twenty bushels of wheat in England would sell for twenty-eight dollars; therefore, there would be twenty-two dollars left for the cost of cultivation and profit.

A French writer on scientific agriculture has employed figures very similar to the above, to show how French farmers may grow wheat at less than one dollar per bushel. At this price they might certainly defy the compet.i.tion of the United States. It is one thing, however, to grow crops in a lecture room, and quite another to grow them in a field. In dealing with artificial manures, furnis.h.i.+ng phosphoric acid, potash, and nitrogen, we have substances which act upon the soil in very different ways. Phosphate of lime is a very insoluble substance, and requires an enormous amount of water to dissolve it. Salts of potash, on the other hand, are very soluble in water, but form very insoluble compounds with the soil. Salts of ammonia and nitrate of soda are perfectly soluble in water. When applied to the land, the ammonia of the former substance forms an insoluble compound with the soil, but in a very short time is converted into nitrate of lime; and with this salt and nitrate of soda, remains in solution in the soil water until they are either taken up by the plant or are washed away into the drains or rivers.

Crops evaporate a very large amount of water, and with this water they attract the soluble nitrate from all parts of the soil. Very favorable seasons are therefore those in which the soil is neither too dry nor too wet; as in one case the solution of nitrate becomes dried up in the soil, in the other it is either washed away, or the soil remains so wet that the plant cannot evaporate the water sufficiently to draw up the nitrates which it contains.

The amount of potash and phosphoric acid dissolved in the water is far too small to supply the requirements of the plant, and it is probable that what is required for this purpose is dissolved by some direct action of the roots of the plant on coming in contact with the insoluble phosphoric acid and potash in the soil.

In support of this view, I may mention that we have clear evidence in some of our experiments of the wheat crop taking up both phosphates and potash that were applied to the land thirty years ago.

To suppose, therefore, that, if the ingredients which exist in twenty bushels of wheat and its straw, are simply applied to a barren soil, the crop will be able to come in contact with, and take up these substances, is to a.s.sume what certainly will not take place.

I have often expressed an opinion that arable land, could not be cultivated profitably by means of artificial manures, unless the soil was capable of producing, from its own resources, a considerable amount of produce; still the question had never up to this time come before me in a distinct form as one upon which I had to decide one way or the other. I had, however, no hesitation in coming to the conclusion, that grain crops could never be grown at a profit upon my relation's land, and that consequently, for some years, it would be better to give up the attempt, and try to improve the pasture.

After what I have said about the insolubility of potash and phosphoric acid, it may possibly be asked--why not give a good dose of these substances at once, as they do not wash out of the soil--say enough to grow sixty crops of grain, and apply the nitrate, or ammonia every year in just sufficient amounts to supply the wants of the crop?

The objections to this plan are as follows: a.s.suming the most favorable conditions of climate, and the largest possible produce, the wheat could certainly not take up the whole of the thirty-two pounds of nitrogen applied, and the crop which requires nearly one pound of nitrogen in every one hundred pounds of gross produce, would be certainly less than three thousand two hundred pounds, if supplied with only thirty-two pounds of nitrogen. If we take the total produce of the best and worst wheat crop, grown during the forty years of our experiments, we shall arrive at a better understanding in the matter. The following are the figures:

Weight of Dry Produce of Wheat Per Acre.

_Straw and Grain._ 1863 9330 lbs.

1879 3859 "

In order to ascertain the increase due to the nitrogen of the salts of ammonia or nitrate of soda, we must deduct from the crop the produce obtained, where mineral manures without nitrogen were used. In 1863 this amount was three thousand pounds, and in 1879 it was one thousand two hundred pounds. Deducting these amounts from the gross produce in each case, leaves six thousand three hundred and thirty as the produce due to the nitrogen in the season of 1863, and two thousand six hundred and fifty-nine as the produce due to the nitrogen in 1879.

But in each case we applied the same amount of nitrogen, eighty-seven pounds; and as the amount of nitrogen in a wheat crop, as carted from the field, contains less than one per cent. of nitrogen, it is evident that if all that was contained in the manure had been taken up by the plant, the increased crop should have weighed eight thousand seven hundred pounds instead of six thousand three hundred and thirty. Thus even in our best year, some of the nitrogen applied failed to produce growth; and when we come to the bad year we find that only twenty-six and a half pounds were taken up out of the eighty-seven pounds applied, thus leaving more than two-thirds of the whole unaccounted for.

Seasons are only occasionally either very bad or very good. What we call an average season does not differ very much from the mean of the best and worst years, which in this case would be represented by a crop of four thousand four hundred and ninety-four pounds, containing nearly forty-five pounds of nitrogen. I may say that, although I have employed one per cent. to avoid fractions in my calculations, strictly speaking three-quarters of a per cent. would more nearly represent the real quant.i.ty. If, however, on the average, we only obtain about forty-five pounds from an application of about eighty-seven pounds of nitrogen, it is evident that not more than one-half of the amount applied enters into the crop.

Now in dealing with a substance of so costly a nature as ammonia, or nitrate of soda--the nitrogen contained in which substances cannot cost much less than twenty-five cents per pound by the time it is spread upon the land, it becomes a question of importance to know what becomes of the other half, or the residue whatever it may be, which has not been taken up by the crop. Part is undoubtedly taken up by the weeds which grow with the wheat, and after the wheat has been cut. Part sinks into the sub-soil and is washed completely away during the winter.

I, myself, am disposed to think that the very great difference in the size of the Indian corn crops, as compared with the wheat crops in the States, is partly accounted for by their greater freedom from weeds, which are large consumers of nitric acid, and, in the case of the wheat crop, frequently reduce the yield by several bushels per acre. It must, however, be borne in mind that, though the wheat is robbed of its food where there are weeds, still if there were no weeds, the amount of nitric acid which the crop could not get hold of, would, in all probability, be washed out of the soil during the ensuing winter. I come to the conclusion, therefore, that the nitrogen alone, which would be required to produce one bushel of wheat, would cost not much less than fifty cents; and that, in consequence, wheat-growing by means of artificial manures, will not pay upon very poor land.

I have said that the land, about which I was consulted, had not been plowed for several years, and that although nature had done all she could to clothe the soil with vegetation, the most disheartening feature in the case was, the poverty of the weeds. A thistle may be a giant or a dwarf, according to circ.u.mstances; here they were all dwarfs. The plaintain, which I believe is sometimes sown in these districts for food, has a very deep root; here the plants were abundant, but the leaves were very small and lay so close to the ground, that, as the manager informed me, "the sheep were often injured from the amount of sand which they swallowed with the leaves when feeding."

At Rothamsted, the a.n.a.lyses of the rain water pa.s.sing through the ordinary soil of one of my fields, which has been kept free from vegetation, have shown that the amount of nitric acid liberated in a soil, and washed out each year, is very large. Taking the ten years during which these special experiments have been in progress, I should think that the loss of nitrogen would be equal to, or possibly exceed, the amount of that substance removed by the average crops grown in the United States.

The results obtained by the rain gauges, are further completely confirmed by those in an adjoining field, where wheat and fallow have been grown alternately for twenty-seven years. The liberation of nitric acid, during the year of rest, produced for a time a large growth of wheat, but it was done at a very great waste of the fertility of the soil, and the produce is now, in proportion, considerably lower than that grown on the continuously unmanured land.

These results, if they are to be accepted as correct, must bring about a very considerable change in the generally received views in regard to fertility. We not only see more clearly the connection between a former vegetation and the stored up fertility in our soil, but we also see the importance of vegetation at the present day, as the only means by which the loss of nitric acid is prevented. The more completely the land is covered with vegetation, and the more growth there is, the greater will be the evaporation of water, and the less will be the loss of nitric acid by drainage.

I was not at all surprised to find, that the surface soil of a wood on my farm, was poorer in nitrogen than the soil of an old permanent pasture, to which no manure had been applied for twenty-five years, though during the whole period, the crop of hay had been removed every year from the land. The wood to which I refer is covered with oak, centuries old, and the foliage is so dense that but little underwood or other vegetation can grow beneath it. If both the wood and the pasture were put into arable cultivation, I have no doubt that the pasture would prove much more fertile than the wood land.

In our experiments on permanent pasture, it has been observed that the character of the herbage is mainly dependent on the food supplied.

Weeds, and inferior gra.s.ses, can hold their own as long as poverty exists, but with a liberal supply of manure, the superior gra.s.ses overgrow and drive out the bad gra.s.ses and weeds. In consequence of the low price of wheat a good deal of land in England has been laid down to permanent pasture, and much money has been spent in cleaning the land preparatory to sowing the gra.s.s-seeds. I have on more occasions than one, suggested that the money employed in this process would be better expended in manure, by which the weeds would be "improved" off the face of the land. While walking over the abandoned portion of these estates I explained my views upon this point to the manager. They were, however, received with the usual skepticism, and the rejoinder that "there was only one way of getting rid of the weeds, which was by the plow and fire."

There is nothing that speaks to me so forcibly as color in vegetation; when travelling by rail, I do not require to be told that such a farm is, or is not, in high condition, or that we are pa.s.sing through a fertile or infertile district. There is a peculiar green color in vegetation which is an unmistakable sign that it is living upon the fat of the land. I need hardly say that, in this case, the color of the vegetation gave unmistakable signs of the poverty of the soil; but in the midst of the dingy yellowish-green of the herbage, I came upon one square of bright green gra.s.s. In answer to my enquiry I was told that, a "lambing-fold had been there last year," and my informant added his opinion, "that the manure would be so strong that it would kill anything!" It had certainly killed the weeds, but in their place, some good gra.s.ses had taken possession of the soil.

The plan I proposed to adopt was, to spend no more money on tillage operations, but to endeavor to improve the pasture by giving to it the food necessary to grow good gra.s.ses, sowing at the same time a small quant.i.ty of the best seeds. I further suggested that a flock of sheep should be allowed to run over the whole of the land by day, and be folded there every night--about one pound of cotton-seed cake per head being allowed daily. By this means, as the fold would be moved every day, the amount of manure deposited on the soil could be estimated.

If there were a hundred sheep, receiving one pound of decorticated cotton-seed cake per head, daily, and the hurdles were arranged to enclose a s.p.a.ce of twenty-five by twenty yards, in the course of ten days an acre of land would have received manure from one thousand pounds of cake; which amount would supply seventy-seven pounds of nitrogen, sixty-eight pounds of phosphate of lime, and thirty-two pounds of potash. This amount of cake would cost about sixteen dollars.

As regards the value of the cake as a food, it is somewhat difficult to form an estimate; but it takes nine or ten pounds of dry food--say roots, cake, and hay--to produce an increase of one pound of live weight in sheep. The cake has certainly a higher feeding value, than either hay or roots, but I will here give it only the same value, and consider that one hundred and ten pounds of increase of the animal was obtained by the consumption of the one thousand pounds of cake. The value of the increase of the live weight would be in England fully eleven dollars, leaving five dollars as the cost of the manure. Now the cake furnished seventy-seven pounds of nitrogen alone, which, if purchased in an artificial manure, would have cost nineteen dollars; and the other substances supplied by the cake, would have cost from four to five dollars more. The manures required, therefore, would be obtained much more cheaply by this than by any other process.

Labor would be saved by not cultivating the land. Manure would be saved by subst.i.tuting vegetation which grows under or above ground, almost all the year round. And, by feeding the stock with cake, the necessary fertility would be obtained at the lowest possible cost.

It is probable that the land would require this treatment to be repeated for several years, before there would be a fair growth of gra.s.s. The land might then be broken up and one grain crop be taken, then it might again be laid down to gra.s.s.

Hitherto, I have considered a case where fertility is almost absent from the land, this, however, is an exception, as agriculture generally is carried on upon soils which contain large stores of fertility, though they may be very unequally distributed. By a.n.a.lysis of the soil we can measure the total amount of fertility which it contains, but we are left in ignorance in regard to the amount of the ingredients which are in such a form that the crops we cultivate can make use of them.

At Rothamsted, among my experiments on the growth of continuous wheat, at the end of forty years, the soil supplied with salts of ammonia has yielded, during the whole time, and still continues to yield, a larger produce than is obtained by a liberal supply of phosphates and alkaline salts without ammonia.

When we consider that every one hundred pounds of wheat crop, as carted to the stack, contains about five per cent. of mineral matter, and one per cent. of nitrogen, it is impossible to avoid the conclusion that my soil has a large available balance of mineral substances which the crop could not make use of for want of nitrogen. The crop which has received these mineral manures now amounts to from twelve to thirteen bushels per acre, and removes from the land about sixteen pounds of nitrogen every year.

a.n.a.lyses of the soil show that, even after the removal of more than thirty crops in succession, without any application of manure containing ammonia, the soil still contains some thousands of pounds of nitrogen.

This nitrogen is in combination with carbon; it is very insoluble in water, and until it becomes separated from the carbon, and enters into combination with oxygen, does not appear to be of any use to the crop.

The combination of nitrogen with oxygen, is known as nitric acid. The nitric acid enters into combination with the lime of the soil, and in this form becomes the food of plants.

From its great importance in regard to the growth of plants, nitric acid might be called the main spring of agriculture, but being perfectly soluble in water, it is constantly liable to be washed out of the soil.

In the experiment to which I have referred above--where wheat is grown by mineral manures alone--we estimate that, of the amount of nitric acid liberated each year, not much more than one-half is taken up by the crop.

The wheat is ripe in July, at which time the land is tolerably free from weeds; several months, therefore, occur during which there is no vegetation to take up the nitric acid; and even when the wheat is sown at the end of October, much nitric acid is liable to be washed away, as the power of the plant to take up food from the soil is very limited until the spring.

The formation of nitric acid, from the organic nitrogen in the soil, is due to the action of a minute plant, and goes on quite independent of the growth of our crops. We get, however, in the fact an explanation of the extremely different results obtained by the use of different manures. One farmer applies lime, or even ground limestone to a soil, and obtains an increase in his crops; probably he has supplied the very substance which has enabled the nitrification of the organic nitrogen to increase; another applies potash, a third phosphates; if either of these are absent, the crops cannot make use of the nitric acid, however great may be the amount diffused through the soil.

It may possibly be said that the use of mineral manures tends to exhaust the soil of its nitrogen; this may, or may not, be true; but even if the minerals enable the crop to take up a larger amount of the nitric acid found in the soil year by year, this does not increase the exhaustion, as the minerals only tend to arrest that which otherwise might be washed away.

We must look upon the organic nitrogen in the soil, as the main source of the nitrogen which grows our crops. Whatever may be the amount derived from the atmosphere, whether in rain, or dew; or from condensation by the soil, or plants, it is probable that, where the land is in arable cultivation, the nitrogen so obtained, is less than the amount washed out of the soil in nitric acid. Upon land which is never stirred by the plow, there is much less waste and much less activity.

The large increase in the area of land laid down to permanent pasture in England, is not due alone to the fall in the price of grain. The reduction of fertility in many of the soils, which have been long under the plow, is beginning to be apparent. Under these circ.u.mstances a less exhausting course of treatment becomes necessary, and pasture, with the production of meat, milk, and b.u.t.ter, takes the place of grain fields.

APPENDIX.