| Insoluble matter | 63.70 |
| Potash (K₂O) | 1.06 |
| Soda (Na₂O) | .22 |
| Lime (CaO) | 4.97 |
| Magnesia (MgO) | 2.43 |
| Br. ox. of Manganese (Mn₃O₄) | .14 |
| Peroxid of Iron (Fe₂O₃) | 5.80 |
| Alumina (Al₂O₃) | 6.86 |
| Phosphoric acid (P₃O₅) | .16 |
| Sulfuric acid (SO₃) | .13 |
| Carbonic acid (CO₂) | 7.45 |
| Water and organic matter | 9.98 |
| Humus | 1.17 |
| “ Nitrogen | 11.11 |
| “ “ per cent. in soil | .13 |
| Hygroscopic Moisture absorbed at °C | 2.63 |
DISCUSSION OF THE TABLE.
Lime.—Considering in this table, first, lime, a glance at the columns for the two regions shows a surprising and evidently intrinsic and material difference, approximating in the average by totals to the proportion of 1 to 11; in the average by states, 1 to 14½. This difference is so great that no accidental errors in the selection or analysis of the soils can to any material degree weaken the overwhelming proof of the correctness of the inference drawn upon theoretical grounds, viz., that the soils of the arid regions must be richer in lime than those of the humid countries. For the differences in derivation would, in view of the wide prevalence of limestone formations in the humid regions concerned, produce exactly the reverse condition of things from that which is actually found to exist; and if further proof were needed it can readily be found in the detailed discussion of the analyses of the soils of the arid areas forming the contrast. This shows that for instance, in Washington highly calcareous soils are directly derived from the black basaltic rocks; while similarly, calcareous lands are found in California to be the outcome of the decomposition of granites, diorites, lavas, clay-shales and sandstones.
It is not easy to overrate the importance of this feature of the soils of the arid region, as it is intimately connected with other theoretically and practically important facts, in part already mentioned.
Summary of Effects of Lime Carbonate in Soils.—It is best to summarize, briefly, at this point, the advantages (and possible disadvantages), resulting from the presence of a proper amount of lime carbonate in soils, so far as these are at present understood.
Physically, even a small amount of lime carbonate, by its solubility in the carbonated soil-water, will act most beneficially in causing the flocculation of clay and in the subsequent conservation of the flocculent or tilth condition, by acting as a light cement holding the soil-crumbs together when the capillary water has evaporated; thus favoring the penetration of both water and air, and of the roots themselves. It should be added that according to the experience of the writer, amounts of lime carbonate in excess of 2% do not add to the favorable effects, except as would so much sand.
As to chemical effects, among the most important are:—
1. The maintenance of the neutrality of the soil, by the neutralization of acids formed by the decay of organic matter, or otherwise.
2. The maintenance, in connection with the proper degrees of moisture and warmth, of the conditions of abundant bacterial life ([see above, chapter 9, p. 146]); more especially those of nitrification, thus supplying the readily assimilable form of nitrogen. Also in favoring the development and activity of the root bacteria of legumes, and of the other nitrogen-gathering bacteria, such as Azotobacter ([ibid. p. 156]).
3. The rendering available, directly or indirectly, of relatively small percentages of plant-food, notably phosphoric acid and potash; as shown in the preceding pages.