Paring and burning, instead of being an antiquated operation, is a practice the advantages of which are fully confirmed and explained by modern chemical science.
Paring and burning, to judge from our own experience, had the effect of converting some of the hard limestone brash into lime, in which case it broke up by the influences of air and rain, and so restored the lime and alumina which mostly exist together in limestone, the former of which is quickly lost in thin soils,—so much so, indeed, that not unfrequently the whole depth of soil, even upon a limestone, will often be curiously devoid of lime, which is a necessary ingredient in the constitution of a clover crop.
Again, we should conclude that the operation under discussion, from its decomposing that dark vegetable matter called humus, which is always found in large quantities on some of the soils which are called “dead,” from their inability to produce crops, and which often cause astonishment that such black, nice-looking earth should be unproductive. Now this soil, though it would favour the growth of some species of peat-loving plants, as Ling, Heath, &c., is not suitable for clover, as the wild plant is curiously absent from peaty positions.
Professor Voelcker remarks that “the excess of undecomposed organic matters in soils is decidedly injurious to vegetation. Roots, stems, and other vegetable matters remain buried in the ground for years without undergoing decomposition, and if we attentively study the subjoined analysis of soil in the neighbourhood of Cirencester, well adapted for burning, we shall see how the lime, alumina, and organic matter might be beneficially affected by the process:—
| ANALYSIS OF SOIL ADAPTED FOR BURNING, BY PROFESSOR VOELCKER. | |||
| Moisture | ·93 | ||
| Organic matter | 10 | ·67 | |
| Oxides of iron and alumina | 13 | ·40 | |
| Carbonate of lime with a little sulphate of lime | 23 | ·90 | |
| Carbonate of magnesia | 1 | ·10 | |
| Phosphoric acid | trace | ||
| Potash | ·38 | ||
| Soda | ·13 | ||
| Insoluble silicious matter | 49 | ·66 | |
| 100 | ·17 | ” | |
The ashes, however, are obtained by burning a thin slice pared from the surface of the land, so that they are derived from surface-soil and vegetable matter, the latter often yielding a sufficient amount of phosphoric acid with which to procure a crop, and, what is all important for us to consider is, that this phosphorus, the alkalies, and lime, are rendered by the burning in a state just fitted for the growth of the plants that are to be grown upon them; whereas, before the process, these ingredients were in a measure locked up, so that plants could not grow for the want of sustenance; not that it was not in the soil, but that it was insoluble. If, then, clover or any other plant had not succeeded, it would have been called “clover-sick.”
The following analysis of vegetable ashes from a field in the neighbourhood of Cirencester will well repay attentive consideration, as illustrating these points:—
| ANALYSIS OF ASHES FROM PARING AND BURNING, BY PROFESSOR VOELCKER. | |||
| Moisture and organic matter | 9 | ·12 | |
| Oxides of iron and alumina | 14 | ·56 | |
| Carbonate of lime | 17 | ·17 | |
| Sulphate of lime | 1 | ·73 | |
| Magnesia | ·40 | ||
| Chloride of sodium | ·08 | ||
| Chloride of potassium | ·32 | ||
| Potash | 1 | ·44 | |
| Phosphoric acid | 1 | ·84 | |
| Equal to bone earth | (3 | ·98 | ) |
| Soluble silica (soluble in potash) | 8 | ·70 | |
| Insoluble silicious matter | 44 | ·64 | |
| 100 | ·00 | ||
Now, that land so burnt and containing such ingredients would, after the process, refuse to grow clovers we cannot at all believe; but we do know that some of the land of a like composition will not grow even a crop of turnips until prepared as described; and though the taking a subsequent barley crop off before the clover would not tend to the improvement of the latter, it will be too often because the barley has taken all the available manurial matter, so that there is little left for the clover to feed upon. In such cases we have seen the clover saved by top dressing. Paring and burning had also a salutary effect upon the clover crop in the destruction which it wrought to various insect pests, and more especially the wire-worm, which now makes such increasing inroads upon our crops of wheat and barley, and so afterwards in the clover; so that bare patches, often of great extent, will be the consequence in every crop in the rotation. Now, these bare patches in the clover crop are often appealed to as evidence of clover-sickness, whilst we do not at the same time say that land is wheat-sick or barley-sick.
Insects, indeed, are yearly becoming more destructive, not only on account of the difference in the mode of farming, but greatly from the determined destruction of birds. The food of birds is in general very mixed, but at one season of the year, when they are breeding, they are most industrious destroyers of insects; but it is just at this time that they are kept from the crops, exactly when insects are working the most mischief: hence, then, as the exigencies of a small growing family become more and more pressing, birds are driven to feed their young upon seeds, fruits, buds, and other vegetable matters, as unsuitable to build up the constitution of the young bird as bread diet for an infant.