“This difference in the amount of accumulated nitrogen in clover-land, appears still more strikingly on comparing the total amounts of nitrogen per acre in the different sections of the two portions of the 11-acre field.
| First six inches. Lbs. | Second six inches. Lbs. | Third six inches. Lbs. | |
|---|---|---|---|
| I. In soil, clover twice mown* | 3,350 | 1,875 | 1,325 |
| II. In soil, clover once mown and seeded afterwards† | 4,725 | 3,350 | 2,225 |
| Equal to ammonia: | |||
| * I. Clover twice mown | 4,050 | 2,275 | 1,600 |
| † II. Clover seeded | 5,725 | 4,050 | 2,700 |
| Lbs. | ||
|---|---|---|
I. Nitrogen in roots of clover twice mown | 24½ | |
II. Nitrogen in clover, once mown, and grown for seedafterwards | 51½ | |
I. Weight of dry roots per acre from Soil I | 1,493½ | |
II. Weight of dry roots per acre from Soil II | 3,622 | |
Total amount of nitrogen in 1 acre, 12 inches deep of Soil I* | 5,249¼ | |
Total amount of nitrogen in 1 acre, 12 inches deep of Soil II† | 8,126¼ | |
Excess of nitrogen in an acre of soil 12 inches deep, calculated asammonia in part of field, mown once and then seeded | 3,592½ | |
| * Equal to ammonia | 6,374½ | |
| † Equal to ammonia | 9,867 | |
“It will be seen that not only was the amount of large clover-roots greater in the part where clover was grown for seed, but that likewise the different layers of soil were in every instance richer in nitrogen after clover-seed, than after clover mown twice for hay.
“Reasons are given in the beginning of this paper which it is hoped will have convinced the reader, that the fertility of land is not so much measured by the amount of ash constituents of plants which it contains, as by the amount of nitrogen, which, together with an excess of such ash constituents, it contains in an available form. It has been shown likewise, that the removal from the soil of a large amount of mineral matter in a good clover-crop, in conformity with many direct field experiments, is not likely in any degree to affect the wheat-crop, and that the yield of wheat on soils under ordinary cultivation, according to the experience of many farmers, and the direct and numerous experiments of Messrs. Lawes and Gilbert, rises or falls, other circumstances being equal, with the supply of available nitrogenous food which is given to the wheat. This being the case, we can not doubt that the benefits arising from the growth of clover to the succeeding wheat, are mainly due to the fact that an immense amount of nitrogenous food accumulates in the soil during the growth of clover.
“This accumulation of nitrogenous plant-food, specially useful to cereal crops, is, as shown in the preceding experiments, much greater when clover is grown for seed, than when it is made into hay. This affords an intelligible explanation of a fact long observed by good practical men, although denied by others who decline to accept their experience as resting upon trustworthy evidence, because, as they say, land cannot become more fertile when a crop is grown upon it for seed, which is carried off, than when that crop is cut down and the produce consumed on the land. The chemical points brought forward in the course of this inquiry, show plainly that mere speculation as to what can take place in a soil, and what not, do not much advance the true theory of certain agricultural practices. It is only by carefully investigating subjects like the one under consideration, that positive proofs are given, showing the correctness of intelligent observers in the fields. Many years ago, I made a great many experiments relative to the chemistry of farm-yard manure, and then showed, amongst other particulars, that manure, spread at once on the land, need not there and then be plowed in, inasmuch as neither a broiling sun, nor a sweeping and drying wind will cause the slightest loss of ammonia; and that, therefore, the old-fashioned farmer who carts his manure on the land as soon as he can, and spreads it at once, but who plows it in at his convenience, acts in perfect accordance with correct chemical principles involved in the management of farm-yard manure. On the present occasion, my main object has been to show, not merely by reasoning on the subject, but by actual experiments, that the larger the amounts of nitrogen, potash, soda, lime, phosphoric acid, etc., which are removed from the land in a clover-crop, the better it is, nevertheless, made thereby for producing in the succeeding year an abundant crop of wheat, other circumstances being favorable to its growth.
“Indeed, no kind of manure can be compared in point of efficacy for wheat, to the manuring which the land gets in a really good crop of clover. The farmer who wishes to derive the full benefit from his clover-lay, should plow it up for wheat as soon as possible in the autumn, and leave it in a rough state as long as is admissible, in order that the air may find free access into the land, and the organic remains left in so much abundance in a good crop of clover be changed into plant-food; more especially, in other words, in order that the crude nitrogenous organic matter in the clover-roots and decaying leaves, may have time to become transformed into ammoniacal compounds, and these, in the course of time, into nitrates, which I am strongly inclined to think is the form in which nitrogen is assimilated, par excellence by cereal crops, and in which, at all events, it is more efficacious than in any other state of combination wherein it may be used as a fertilizer.
“When the clover-lay is plowed up early, the decay of the clover is sufficiently advanced by the time the young wheat-plant stands in need of readily available nitrogenous food, and this being uniformly distributed through the whole of the cultivated soil, is ready to benefit every single plant. This equal and abundant distribution of food, peculiarly valuable to cereals, is a great advantage, and speaks strongly in favor of clover as a preparatory crop for wheat.
“Nitrate of soda, an excellent spring top-dressing for wheat and cereals in general, in some seasons fails to produce as good an effect as in others. In very dry springs, the rainfall is not sufficient to wash it properly into the soil and to distribute it equally, and in very wet seasons it is apt to be washed either into the drains or into a stratum of the soil not accessible to the roots of the young wheat. As, therefore, the character of the approaching season can not usually be predicted, the application of nitrate of soda to wheat is always attended with more or less uncertainty.
“The case is different, when a good crop of clover-hay has been obtained from the land on which wheat is intended to be grown afterwards. An enormous quantity of nitrogenous organic matter, as we have seen, is left in the land after the removal of the clover-crop; and these remains gradually decay and furnish ammonia, which at first and during the colder months of the year, is retained by the well known absorbing properties which all good wheat-soils possess. In spring, when warmer weather sets in, and the wheat begins to make a push, these ammonia compounds in the soil are by degrees oxidized into nitrates; and as this change into food peculiarly favorable to young cereal plants, proceeds slowly but steadily, we have in the soil itself, after clover, a source from which nitrates are continuously produced; so that it does not much affect the final yield of wheat, whether heavy rains remove some or all of the nitrate present in the soil. The clover remains thus afford a more continuous source from which nitrates are produced, and greater certainty for a good crop of wheat than when recourse is had to nitrogenous top-dressings in the spring.