Talks on Manures Part 20

"Of course, these ill.u.s.trations," said the Doctor, "do not give us any clear idea of _how_ the clover-plants take up food. We must recollect that the roots of plants take up their food in solution; and it has just occurred to me that, possibly, Mr. Lawes' experiments on the amount of water given off by plants during their growth, may throw some light on the subject we are discussing."

"Mr. Lawes found," continued the Doctor, "that a wheat-plant, from March 19 to June 28, or 101 days, evaporated through its leaves, etc., 45,713 grains of water; while a clover-plant, standing alongside, and in precisely similar condition, evaporated 55,093 grains. The clover was cut June 28, when in full bloom. The wheat-plant was allowed to grow until ripe, Sept. 7. From June 28 to Sept. 7, or 72 days, the wheat-plant evaporated 67,814 grains."

"One moment," said the Deacon; "as I understand, the clover-plant evaporated more water than the wheat-plant, until the 28th of June, but that during the next 71 days, the wheat-plant evaporated more water than it had during the previous 101 days."

"Yes," said I, "and if these facts prove nothing else, they at least show that there is a great difference between wheat and clover. I was at Rothamsted when these experiments were made. During the first nine days of the experiment, the clover-plant evaporated 399.6 grains of water; while the wheat-plant, standing alongside, evaporated only 128.7 grains.

In other words, the clover-plant evaporated three times as much water as the wheat-plant. During the next 31 days, the wheat-plant evaporated 1,267.8 grains, and the clover-plant 1,643.0 grains; but during the next 27 days, from April 28 to May 25, the wheat-plant evaporated 162.4 grains of water per day, while the clover-plant only evaporated 109.2 grains per day. During the next 34 days, from May 25 to June 28, the wheat-plant evaporated 1,177.4 grains per day, and the clover-plant 1,473.5 grains per day."

"In June," said the Deacon, "the clover evaporates ten times as much water per day as it did in May. How much water would an acre of clover evaporate?"

"Let Charley figure it out," said the Doctor. "Suppose each plant occupies 10 square inches of land; there are 6,272,640 square inches in an acre, and, consequently, there would be 627,264 clover-plants on an acre. Each plant evaporated 1,473.5 grains per day, and there are 7,000 grains in a pound."

Charley made the calculation, and found that an acre of clover, from May 25 to June 28, evaporated 528,598 lbs. of water, or 15,547 lbs. per day.

A much more accurate way of ascertaining how much water an acre of clover evaporates is afforded us by these experiments. After the plants were cut, they were weighed and a.n.a.lyzed; and it being known exactly how much water each plant had given off during its growth, we have all the facts necessary to tell us just how much a crop of a given weight would evaporate. In brief, it was found that for each pound of dry substance in the wheat-plant, 247.4 lbs. of water had been evaporated; and for each pound in the clover-plant, 269.1 lbs.

An acre of wheat of 15 bushels per acre of grain, and an equal weight of straw, would exhale during the spring and summer 177 tons of water, or calculated on 172 days, the duration of the experiment, 2,055 lbs. per day.

An acre of clover that would make two tons of hay, would pa.s.s off through its leaves, in 101 days, 430 tons of water, or 8,600 lbs. per day--more than four times as much as the wheat.

These figures show that, from an agricultural point of view, there is a great difference between, wheat and clover; and yet I think the figures do not show the whole of the difference. The clover was cut just at the time when the wheat-plant was entering on its period of most rapid growth and exhalation, and, consequently, the figures given above probably exaggerate the amount of water given off by the wheat during the early part of the season. It is, at any rate, quite clear, and this is all I want to show, that an acre of good clover exhales a much larger amount of water from spring to hay-harvest than an acre of wheat.

"And what," said the Deacon, who was evidently getting tired of the figures, "does all this prove?"

The figures prove that clover can drink a much greater quant.i.ty of water during March, April, May, and June, than wheat; and, consequently, to get the same amount of food, it is not necessary that the clover should have as much nitrogen, phosphoric acid, potash, etc., in the water as the wheat-plant requires. I do not know that I make myself understood.

"You want to show," said the Deacon, "that the wheat-plant requires richer food than clover."

Yes, I want to show that, though clover requires _more_ food per day than wheat, yet the clover can drink such a large amount of water, that it is not necessary to make the "sap of the soil" so rich in nitrogen, phosphoric acid, and potash, for clover, as it is for wheat. I think this tells the whole story.

Clover is, or may be, the grandest renovating and enriching crop commonly grown on our farms. It owes its great value, not to any power it may or may not possess of getting nitrogen from the atmosphere, or phosphoric acid and potash from the subsoil, but princ.i.p.ally, if not entirely, to the fact that the roots can drink up such a large amount of water, and live and thrive on very weak food.

HOW TO MAKE A FARM RICH BY GROWING CLOVER.

Not by growing the clover, and selling it. Nothing would exhaust the land so rapidly as such a practice. We must either plow under the clover, let it rot on the surface, or pasture it, or use it for soiling, or make it into hay, feed it out to stock, and return the manure to the land. If clover got its nitrogen from the atmosphere, we might sell the clover, and depend on the roots left in the ground, to enrich the soil for the next crop. But if, as I have endeavored to show, clover gets its nitrogen from a weak solution in the soil, it is clear, that though for a year or two we might raise good crops from the plant-food left in the clover-roots, yet we should soon find that growing a crop of clover, and leaving only the roots in the soil, is no way to permanently enrich land.

I do not say that such a practice will "exhaust" the land. Fortunately, while it is an easy matter to impoverish land, we should have to call in the aid of the most advanced agricultural science, before we could "exhaust" land of its plant-food. The free use of Nitrate of Soda, or Sulphate of Ammonia, might enable us to do something in the way of exhausting our farms, but it would reduce our balance at a bank, or send us to the poor-house, before we had fully robbed the land of its plant-food.

To exhaust land, by growing and selling clover, is an agricultural impossibility, for the simple reason that, long before the soil is exhausted, the clover would produce such a poverty-stricken crop, that we should give up the attempt.

We can make our land poor, by growing clover, and selling it; or, we can make our land rich, by growing clover, and feeding it out on the farm.

Or, rather, we can make our land rich, by draining it where needed, cultivating it thoroughly, so as to develope the latent plant-food existing in the soil, and then by growing clover to take up and organize this plant-food. This is how to make land rich by growing clover. It is not, in one sense, the clover that makes the land rich; it is the draining and cultivation, that furnishes the food for the clover. The clover takes up this food and concentrates it. The clover does not create the plant-food; it merely saves it. It is the thorough cultivation that enriches the land, not the clover.

"I wish," writes a distinguished New York gentleman, who has a farm of barren sand, "you would tell us whether it is best to let clover ripen and rot on the surface, or plow it under when in blossom? I have heard that it gave more nitrogen to the land to let it ripen and rot on it, but as I am no chemist, I do not know."

If, instead of plowing under the clover--say the last of June, it was left to grow a month longer, it is quite possible that the clover-roots and seed would contain more nitrogen than they did a month earlier. It was formerly thought that there was a loss of nitrogen during the ripening process, but the evidence is not altogether conclusive on the point. Still, if I had a piece of sandy land that I wished to enrich by clover, I do not think I should plow it under in June, on the one hand, or let it grow until maturity, and rot down, on the other. I should rather prefer to mow the crop just as it commenced to blossom, and let the clover lie, spread out on the land, as left by the machine. There would, I think, be no loss of fertilizing elements by evaporation, while the clover-hay would act as a mulch, and the second growth of clover would be encouraged by it. Mow this second crop again, about the first week in August. Then, unless it was desirable to continue the process another year, the land might be plowed up in two or three weeks, turning under the two previous crops of clover that are on the surface, together with the green-clover still growing. I believe this would be better than to let the clover exhaust itself by running to seed.

CHAPTER XXV.

DR. VLCKER'S EXPERIMENTS ON CLOVER.

In the Journal of the Royal Agricultural Society of England, for 1868, Dr. Vlcker, the able chemist of the Society, and formerly Professor of Agricultural Chemistry, at the Royal Agricultural College at Cirencester, England, has given us a paper "On the Causes of the Benefits of Clover, as a preparatory Crop for Wheat." The paper has been repeatedly and extensively quoted in this country, but has not been as critically studied as the importance of the subject demands.

"Never mind all that," said the Deacon, "tell us what Dr. Vlcker says."

"Here is the paper," said I, "and Charley will read it to us." Charley read as follows:

"Agricultural chemists inform us, that in order to maintain the productive powers of the land unimpaired, we must restore to it the phosphoric acid, potash, nitrogen, and other substances, which enter into the composition of our farm crops; the constant removal of organic and inorganic soil const.i.tuents, by the crops usually sold off the farm, leading, as is well known, to more or less rapid deterioration and gradual exhaustion of the land. Even the best wheat soils of this and other countries, become more and more impoverished, and sustain a loss of wheat-yielding power, when corn-crops are grown in too rapid succession without manure. Hence, the universal practice of manuring, and that also of consuming oil-cake, corn, and similar purchased food on land naturally poor, or partially exhausted by previous cropping.

"Whilst, however, it holds good as a general rule, that no soil can be cropped for any length of time, without gradually becoming more and more infertile, if no manure be applied to it, or if the fertilizing elements removed by the crops grown thereon, be not by some means or other restored, it is, nevertheless, a fact, that after a heavy crop of clover carried off as hay, the land, far from being less fertile than before, is peculiarly well adapted, even without the addition of manure, to bear a good crop of wheat in the following year, provided the season be favorable to its growth. This fact, indeed, is so well known, that many farmers justly regard the growth of clover as one of the best preparatory operations which the land can undergo, in order to its producing an abundant crop of wheat in the following year. It has further been noticed, that clover mown twice, leaves the land in a better condition, as regards its wheat-producing capabilities, than when mown once only for hay, and the second crop fed off on the land by sheep; for, notwithstanding that in the latter instance the fertilizing elements in the clover-crop are in part restored in the sheep excrements, yet, contrary to expectation, this partial restoration of the elements of fertility to the land has not the effect of producing more or better wheat in the following year, than is reaped on land from off which the whole clover-crop has been carried, and to which no manure whatever has been applied.

"Again, in the opinion of several good, practical agriculturists, with whom I have conversed on the subject, land whereon clover has been grown for seed in the preceding year, yields a better crop of wheat than it does when the clover is mown twice for hay, or even only once, and afterwards fed off by sheep."

"I do not think," said the Deacon, "that this agrees with our experience here. A good crop of clover-seed is profitable, but it is thought to be rather hard on land."

"Such," said I, "is the opinion of John Johnston. He thinks allowing clover to go to seed, impoverishes the soil."

Charley, continued to read:

"Whatever may be the true explanation of the apparent anomalies connected with the growth and chemical history of the clover-plant, the facts just mentioned, having been noticed, not once or twice only, or by a solitary observer, but repeatedly, and by numbers of intelligent farmers, are certainly ent.i.tled to credit; and little wisdom, as it strikes me, is displayed by calling them into question, because they happen to contradict the prevailing theory, according to which a soil is said to become more or less impoverished, in proportion to the large or small amount of organic and mineral soil const.i.tuents carried off in the produce."

"That is well said," I remarked, "and very truly; but I will not interrupt the reading."

"In the course of a long residence," continues Dr. Vlcker, "in a purely agricultural district, I have often been struck with the remarkably healthy appearance and good yield of wheat, on land from which a heavy crop of clover-hay was obtained in the preceding year. I have likewise had frequent opportunities of observing, that, as a rule, wheat grown on part of a field whereon clover has been twice mown for hay, is better than the produce of that on the part of the same field on which the clover has been mown only once for hay, and afterwards fed off by sheep.

These observations, extending over a number of years, led me to inquire into the reasons why clover is specially well fitted to prepare land for wheat; and in this paper, I shall endeavor, as the result of my experiments on the subject, to give an intelligible explanation of the fact, that clover is so excellent a preparatory crop for wheat, as it is practically known to be.

"By those taking a superficial view of the subject, it may be suggested that any injury likely to be caused by the removal of a certain amount of fertilizing matter, is altogether insignificant, and more than compensated for, by the benefit which results from the abundant growth of clover-roots, and the physical improvement in the soil, which takes place in their decomposition. Looking, however, more closely into the matter, it will be found that in a good crop of clover-hay, a very considerable amount of both mineral and organic substances is carried off the land, and that, if the total amount of such const.i.tuents in a crop had to be regarded exclusively as a measure for determining the relative degrees in which different farm crops exhaust the soil, clover would have to be described as about the most exhausting crop in the entire rotation.

"Clover-hay, on an average, and in round numbers, contains in 100 parts:

Water 17.0 Nitrogenous substances, (flesh-forming matters)* 15.6 Non-nitrogenous compounds 59.9 Mineral matter, (ash) 7.5 ----- 100.0 ===== * Containing nitrogen 2.5

"The mineral portion, or ash, in 100 parts of clover-hay, consists of:

Phosphoric acid 7.5 Sulphuric acid 4.3 Carbonic acid 18.0 Silica 3.0 Lime 30.0 Magnesia 8.5 Potash 20.0 Soda, chloride of sodium, oxide of iron, sand, loss, etc. 8.7 ----- 100.0 =====

"Let us suppose the land to have yielded four tons of clover-hay per acre. According to the preceding data, we find that such a crop includes 224 lbs. of nitrogen, equal to 272 lbs. of ammonia, and 672 lbs. of mineral matter or ash const.i.tuents.

"In 672 lbs. of clover-ash, we find:

Phosphoric acid 51 lbs.

Sulphuric acid 29 "

Carbonic acid 121 "

Silica 20 "