2. In the second,—a fertile soil, but one which cannot dispense with manure,—there is little soluble saline matter, and in the insoluble portion we see that there are mere traces of potash, soda, and the important acids. It contains also 5 per cent. only of organic matter, and about 2 per cent. of lime, which smaller proportions, together with the deficiencies above stated, remove this soil from the most naturally fertile class to that class which is susceptible, in hands of ordinary skill, of being brought to, and kept in, a very productive condition.
3. In the fine part of the third soil, we observe that there are many more substances deficient than in No. 2. The organic matter amounts apparently to 4 per cent., and there seems to be nearly half a per cent. of lime. But it will be recollected, that this soil contains 40 per cent. of sand, so that in every hundred of soil there are only 60 of the fine matter, of which the composition is presented in the table, or 100 lbs. of the native soil contain only 2½ lbs. of organic matter and ¼ lb. of lime.
But all these wants would not condemn the soil to hopeless barrenness, because in favourable circumstances, and where it was worth the cost, they might all be supplied. But the oxide of iron amounts to 8 per cent. of this fine matter, a proportion of this substance which, in a soil containing so little organic matter, appears, from practical experience, to be incompatible with the healthy growth of cultivated crops. To this soil, therefore, there requires to be added not only those substances of which it is destitute, but such other substances also as shall prevent the injurious effect of the large proportion of oxide of iron.
In these three soils, then, we have examples, first, of one which contains within itself all the elements of fertility; second, of a soil which is destitute, or nearly so, of certain substances,—which, however, can be readily added by the ordinary manures in general use,—and to which the elements of gypsum are especially useful, in aiding it to feed the potato and the turnip; and, third, of a soil not only poor in many of the necessary species of the inorganic food of plants, but too rich in one which, when present in excess, is prejudicial to vegetable life.
This illustration, therefore, will aid the general reader in comprehending how far rigid chemical analysis is fitted to throw light upon the capabilities of soils, and to direct agricultural practice.
SECTION V.—OF THE RELATION THAT EXISTS
BETWEEN THE CHARACTER OF THE SOIL
AND THE KIND OF PLANTS THAT
GROW UPON IT.
The importance of this study of the chemical constitution of soils will, perhaps, be most readily appreciated by a glance at the very different kinds of vegetables which, under the same circumstances, different soils naturally produce.
There are none so little skilled in regard to the capabilities of the soil, as not to be aware that some lands naturally produce abundant herbage or rich crops, while others refuse to yield a nourishing pasture, and are deaf to the often repeated solicitations of the diligent husbandman. There exists, therefore, a universally understood connection between the kind of soil and the kind of plants that naturally grow upon it. It is interesting to observe how close this relation in many cases is.
1. The sands of the sea-shore, and the margins of salt-lakes, are distinguished by their peculiar tribes of salt-loving plants;—the drifted sands more remote from the beach produce their own long waving coarser grass,—while further inland again, other vegetable races appear.
2. Peaty soils laid down to grass, or existing as natural meadows, produce one woolly soft grass almost exclusively (the Holcus lanatus); when limed, again, these same soils become propitious to green crops and produce much straw, but refuse to fill the ear.