Talks on Manures Part 21

Lime 201 "

Magnesia 57 "

Potash 134 "

Soda, chloride of sodium, oxide of iron, sand, etc. 58 "

------------ 672 lbs.

"Four tons of clover-hay, the produce of one acre, thus contain a large amount of nitrogen, and remove from the soil an enormous quant.i.ty of mineral matters, abounding in lime and potash, and containing also a good deal of phosphoric acid.

"Leaving for a moment the question untouched, whether the nitrogen contained in the clover, is derived from the soil, or from the atmosphere, or partly from the one, and partly from the other, no question can arise as to the original source from which the mineral matters in the clover produce are derived. In relation, therefore, to the ash-const.i.tuents, clover must be regarded as one of the most exhausting crops usually cultivated in this country. This appears strikingly to be the case, when we compare the preceding figures with the quant.i.ty of mineral matters which an average crop of wheat removes from an acre of land.

"The grain and straw of wheat contain, in round numbers, in 100 parts:

Grains of Wheat. Straw.

Water 15.0 16.0 Nitrogenous substances, (flesh-forming matter)* 11.1 4.0 Non-nitrogenous substances 72.2 74.9 Mineral matter, (ash) 1.7 5.1 ----- ------ 100.0 100.0 ===== ====== * Containing nitrogen 1.78 .64

"The ash of wheat contains, in 100 parts:

Grain. Straw.

Phosphoric acid 50.0 5.0 Sulphuric acid 0.5 2.7 Carbonic acid Silica 2.5 67.0 Lime 3.5 5.5 Magnesia 11.5 2.9 Potash 30.0 13.0 Soda, chloride of sodium, oxide of iron, sand, etc. 2.0 4.8 ----- ----- Total 100.0 100.0 ===== =====

"The mean produce of wheat, per acre, may be estimated at 25 bushels, which, at 60 lbs. per bushel, gives 1,500 lbs.; and as the weight of the straw is generally twice that of the grain, its produce will be 3,000 lbs. According, therefore, to the preceding data, there will be carried away from the soil:

In 1,500 lbs. of the grain 25 lbs. of mineral food, (in round numbers).

In 3,000 lbs. of the straw 150 lbs. of mineral food, (in round numbers).

--- Total 175 lbs.

"On the average of the a.n.a.lyses, it will be found that the composition of these 175 lbs. is as follows:

------------------------------+-----------+-----------+---------- In the In the grain. straw. Total.

+-----------+-----------+---------- Phosphoric acid 12.5 lbs. 7.5 lbs. 20.0 lbs.

Sulphuric acid 0.1 " 4.0 " 4.1 "

Carbonic acid Silica 0.6 " 100.5 " 101.1 "

Lime 0.9 " 8.2 " 9.1 "

Magnesia 2.9 " 3.0 " 5.9 "

Potash 7.5 " 19.5 " 27.0 "

Soda, chloride of sodium, oxide of iron, sand, etc. 0.5 " 7.3 " 7.8 "

+-----------+-----------+---------- 25. lbs. 150. lbs. 175. lbs.

"The total quant.i.ty of ash const.i.tuents carried off the land, in an average crop of wheat, thus amounts to only 175 lbs. per acre, whilst a good crop of clover removes as much as 672 lbs.

"Nearly two-thirds of the total amount of mineral in the grain and straw of one acre of wheat, consists of silica, of which there is an ample supply in almost every soil. The restoration of silica, therefore, need not trouble us in any way, especially as there is not a single instance on record, proving that silica, even in a soluble condition, has ever been applied to land, with the slightest advantage to corn, or gra.s.s-crops, which are rich in silica, and which, for this reason, may be a.s.sumed to be particularly grateful for it in a soluble state.

Silica, indeed, if at all capable of producing a beneficial effect, ought to be useful to these crops, either by strengthening the straw, or stems of graminaceous plants, or otherwise benefiting them; but, after deducting the amount of silica from the total amount of mineral matters in the wheat produced from one acre, only a trifling quant.i.ty of other and more valuable fertilizing ash const.i.tuents of plants will be left.

On comparing the relative amounts of phosphoric acid, and potash, in an average crop of wheat, and a good crop of clover-hay, it will be seen that one acre of clover-hay contains as much phosphoric acid, as two and one-half acres of wheat, and as much potash as the produce from five acres of the same crop. Clover thus unquestionably removes from the land very much more mineral matter than does wheat; wheat, notwithstanding, succeeds remarkably well after clover.

"Four tons of clover-hay, or the produce of an acre, contains, as already stated, 224 lbs. of nitrogen, or calculated as ammonia, 272 lbs.

"a.s.suming the grain of wheat to furnish 1.78 per cent of nitrogen, and wheat-straw, .64 per cent, and a.s.suming also that 1,500 lbs. of corn, and 3,000 lbs. of straw, represent the average produce per acre, there will be in the grain of wheat, per acre, 26.7 lbs. of nitrogen, and in the straw, 19.2 lbs., or in both together, 46 lbs. of nitrogen; in round numbers, equal to about 55 lbs. of ammonia, which is only about one-fifth the quant.i.ty of nitrogen in the produce of an acre of clover.

Wheat, it is well known, is specially benefited by the application of nitrogenous manures, and as clover carries off so large a quant.i.ty of nitrogen, it is natural to expect the yield of wheat, after clover, to fall short of what the land might be presumed to produce without manure, before a crop of clover was taken from it. Experience, however, has proved the fallacy of this presumption, for the result is exactly the opposite, inasmuch as a better and heavier crop of wheat is produced than without the intercalation of clover. What, it may be asked, is the explanation of this apparent anomaly?

"In taking up this inquiry, I was led to pa.s.s in review the celebrated and highly important experiments, undertaken by Mr. Lawes and Dr.

Gilbert, on the continued growth of wheat on the same soil, for a long succession of years, and to examine, likewise carefully, many points, to which attention is drawn, by the same authors in their memoirs on the growth of red clover by different manures, and on the Lois Weedon plan of growing wheat. Abundant and most convincing evidence is supplied by these indefatigable experimenters, that the wheat-producing powers of a soil are not increased in any sensible degree by the liberal supply of all the mineral matters, which enter into the composition of the ash of wheat, and that the abstraction of these mineral matters from the soil, in any much larger proportions than can possibly take place under ordinary cultivation, in no wise affects the yield of wheat, provided there be at the same time a liberal supply of available nitrogen within the soil itself. The amount of the latter, therefore, is regarded by Messrs. Lawes and Gilbert, as the measure of the increased produce of grain which a soil furnishes.

"In conformity with these views, the farmer, when he wishes to increase the yield of his wheat, finds it to his advantage to have recourse to ammoniacal, or other nitrogenous manures, and depends more or less entirely upon the soil, for the supply of the necessary mineral or ash-const.i.tuents of wheat, having found such a supply to be amply sufficient for his requirements. As far, therefore, as the removal from the soil of a large amount of mineral soil-const.i.tuents, by the clover-crop, is concerned, the fact viewed in the light of the Rothamsted experiments, becomes at once intelligible; for, notwithstanding the abstraction of over 600 lbs. of mineral matter by a crop of clover, the succeeding wheat-crop does not suffer. Inasmuch, however, as we have seen, that not only much mineral matter is carried off the land in a crop of clover, but also much nitrogen, we might, in the absence of direct evidence to the contrary, be led to suspect that wheat, after clover, would not be a good crop; whereas, the fact is exactly the reverse.

"It is worthy of notice, that nitrogenous manures, which have such a marked and beneficial effect upon wheat, do no good, but in certain combinations, in some seasons, do positive harm to clover. Thus, Messrs.

Lawes and Gilbert, in a series of experiments on the growth of red-clover, by different manures, obtained 14 tons of fresh green produce, equal to about three and three-fourths tons of clover hay, from the unmanured portion of the experimental field; and where sulphates of potash, soda, and magnesia, or sulphate of potash and superphosphate of lime were employed, 17 to 18 tons, (equal to from about four and one-half to nearly five tons of hay), were obtained. When salts of ammonia were added to the mineral manures, the produce of clover-hay was, upon the whole, less than where the mineral manures were used alone. The wheat, grown after the clover, on the unmanured plot, gave, however, 29 bushels of corn, whilst in the adjoining field, where wheat was grown after wheat, without manure, only 15 bushels of corn per acre were obtained. Messrs. Lawes and Gilbert notice especially, that in the clover-crop of the preceding year, very much larger quant.i.ties, both of mineral matters and of nitrogen, were taken from the land, than were removed in the unmanured wheat-crop in the same year, in the adjoining field. Notwithstanding this, the soil from which the clover had been taken, was in a condition to yield 14 bushels more wheat, per acre, than that upon which wheat had been previously grown; the yield of wheat, after clover, in these experiments, being fully equal to that in another field, where large quant.i.ties of manure were used.

"Taking all these circ.u.mstances into account, is there not presumptive evidence, that, notwithstanding the removal of a large amount of nitrogen in the clover-hay, an abundant store of available nitrogen is left in the soil, and also that in its relations towards nitrogen in the soil, clover differs essentially from wheat? The results of our experience in the growth of the two crops, appear to indicate that, whereas the growth of the wheat rapidly exhausts the land of its available nitrogen, that of clover, on the contrary, tends somehow or other to acc.u.mulate nitrogen within the soil itself. If this can be shown to be the case, an intelligible explanation of the fact that clover is so useful as a preparatory crop for wheat, will be found in the circ.u.mstance, that, during the growth of clover, nitrogenous food, for which wheat is particularly grateful, is either stored up or rendered available in the soil.

"An explanation, however plausible, can hardly be accepted as correct, if based mainly on data, which, although highly probable, are not proved to be based on fact. In chemical inquiries, especially, nothing must be taken for granted, that has not been proved by direct experiment. The following questions naturally suggest themselves in reference to this subject: What is the amount of nitrogen in soils of different characters? What is the amount more particularly after a good, and after an indifferent crop of clover? Why is the amount of nitrogen in soils, larger after clover, than after wheat and other crops? Is the nitrogen present in a condition in which it is available and useful to wheat? And lastly, are there any other circ.u.mstances, apart from the supply of nitrogenous matter in the soil, which help to account for the beneficial effects of clover as a preparatory crop for wheat?

"In order to throw some light on these questions, and, if possible, to give distinct answers to at least some of them, I, years ago, when residing at Cirencester, began a series of experiments; and more recently, I have been fortunate enough to obtain the co-operation of Mr.

Robert Valentine, of Leighton Buzzard, who kindly undertook to supply me with materials for my a.n.a.lysis.

"My first experiments were made on a thin, calcareous, clay soil, resting on oolitic limestone, and producing generally a fair crop of red-clover. The clover-field formed the slope of a rather steep hillock, and varied much in depth. At the top of the hill, the soil became very stony at a depth of four inches, so that it could only with difficulty be excavated to a depth of six inches, when the bare limestone-rock made its appearance. At the bottom of the field the soil was much deeper, and the clover stronger, than at the upper part. On the brow of the hill, where the clover appeared to be strong, a square yard was measured out; and at a little distance off, where the clover was very bad, a second square yard was measured; in both plots, the soil being taken up to a depth of six inches. The soil, where the clover was good, may be distinguished from the other, by being marked as No. 1, and that where it was bad, as No. 2.

CLOVER-SOIL NO. 1. (GOOD CLOVER).

"The roots having first been shaken out to free them as much as possible from the soil, were then washed once or twice with cold distilled water, and, after having been dried for a little while in the sun, were weighed, when the square yard produced 1 lb. 10 oz. of cleaned clover-roots, in an air-dry state; an acre of land, or 4,840 square yards, accordingly yielded, in a depth of six inches, 3.44 tons, or 3 tons in round numbers, of clover-roots.

"Fully dried in a water-bath, the roots were found to contain altogether 44.67 per cent of water, and on being burnt in a platinum capsule, yielded 6.089 of ash. A portion of the dried, finely powdered and well mixed roots, was burned with soda lime, in a combustion tube, and the nitrogen contained in the roots otherwise determined in the usual way.

Accordingly, the following is the general composition of the roots from the soil No. 1:

Water 44.675 Organic matter* 49.236 Mineral matter 6.089 ------- 100.000 ======= * Containing nitrogen 1.297 Equal to ammonia 1.575

"a.s.suming the whole field to have produced 3 tons of clover-roots, per acre, there will be 99.636 lbs., or in round numbers, 100 lbs. of nitrogen in the clover-roots from one acre; or, about twice as much nitrogen as is present in the average produce of an acre of wheat."

"That is a remarkable fact," said the Deacon, "as I understand nitrogen is the great thing needed by wheat, and yet the _roots_ alone of the clover, contain twice as much nitrogen as an average crop of wheat. Go on Charley, it is quite interesting."

"The soil," continues Dr. Vlcker, "which had been separated from the roots, was pa.s.sed through a sieve to deprive it of any stones it might contain. It was then partially dried, and the nitrogen in it determined in the usual manner, by combustion with soda-lime, when it yielded .313 per cent of nitrogen, equal to .38 of ammonia, in one combustion; and .373 per cent of nitrogen, equal to .46 of ammonia, in a second determination.

"That the reader may have some idea of the character of this soil, it may be stated, that it was further submitted to a general a.n.a.lysis, according to which, it was found to have the following composition:

General Composition of Soil, No. 1. (Good Clover).

Moisture 18.73 Organic matter* 9.72 Oxide of iron and alumina 13.24 Carbonate of lime 8.82 Magnesia, alkalies, etc. 1.72 Insoluble silicious matter, (chiefly clay) 47.77 ------- 100.00 ======= * Containing nitrogen .313 Equal to ammonia .380

"The second square yard from the brow of the hill, where the clover was bad, produced 13 ounces of air-dry, and partially clean roots, or 1.75 tons per acre. On a.n.a.lysis, they were found to have the following composition:

Clover-Roots, No. 2. (Bad Clover).

Water 55.732 Organic matter* 39.408 Mineral matter, (ash) 4.860 ------- 100.000 ======= * Containing nitrogen .792 Equal to ammonia .901

"The roots on the spot where the clover was very bad, yielded only 31 lbs. of nitrogen per acre, or scarcely one-third of the quant.i.ty which was obtained from the roots where the clover was good.

"The soil from the second square yard, on a.n.a.lysis, was found, when freed from stones by sifting, to contain in 100 parts: