| Tulear. | Maintirano. | Majunga. | ||
|---|---|---|---|---|
| West Coast. | ||||
| Number of Soil. | 253 | 261 | No. 267 | 343 |
| Locality | R. bank of Sakondry north of Tongobory Valley. | Plateau of Antsoamena. | Village of Anhozorabe South of Mandroso. | |
| Sandy soil. | Hill summit. | |||
| Potash (K₂O) | .086 | .015 | .014 | .012 |
| Lime (CaO.) | 4.180 | trace | trace | trace |
| Magnesia (MgO.) | ||||
| Ferric Oxid (Fe₂O₃) | ||||
| Phosphoric Acid (P₂O₅) | .083 | .043 | .011 | .017 |
| Nitrogen (N) | .075 | .051 | .039 | .043 |
| Remarks | Potatoes, manioc, represents soil of whole region. | Manioc, maize, beans, peanuts, coco-trees, mangoes. | Remarkable crops, manioc, rice. | Grasses, tall herbs. |
| Diego Suarez. | ||
|---|---|---|
| N. Coast. | ||
| Number of Soil. | 3 | 331 |
| Locality | Anamakia. | Montagne d’Ambre. |
| Ochr’us earth. | Ochr’us earth. | |
| Potash (K₂O) | .161 | .031 |
| Lime (CaO.) | .620 | trace |
| Magnesia (MgO.) | ||
| Ferric Oxid (Fe₂O₃) | ||
| Phosphoric Acid (P₂O₅) | .380 | .124 |
| Nitrogen (N) | .124 | .177 |
| Remarks | Promises considerable fertility. | Crops,coffee. Good cultural resources. |
| Andevorante. | Ambatondrazaka. | |||
|---|---|---|---|---|
| East Coast. | ||||
| Number of Soil. | 107 | 370 | 81 | 105 |
| Locality | Dist. of Vatomandry. Ampitamafana | Ambaniman- hovinana. | Imeriman- droso. | Sabotsy. |
| Plain valley, sandy soil. | Valley. | Alt 1000 M. | ||
| Potash (K₂O) | .069 | .012 | .490 | .005 |
| Lime (CaO.) | .070 | trace | 1.200 | .070 |
| Magnesia (MgO.) | ||||
| Ferric Oxid (Fe₂O₃) | ||||
| Phosphoric Acid (P₂O₅) | .047 | .161 | 1.566 | .369 |
| Nitrogen (N) | .016 | .254 | .249 | .164 |
| Remarks | Coffee, vanilla, rice, &c., rich red soil. Rep. whole valley. | Very fertile soil. | Amply rich in plant food suited for intensive cultures. | Fertile soil fit for all cultures. |
Be that as it may, the influence of the tropical climate and rainfall upon the composition of these soils is certainly very marked. While gneiss is not credited with producing first-class soils, its usual content of orthoclase feldspar should at least insure a respectable average content of potash; but this, it will be seen, is mostly not the case; and that of lime seems even worse, aside from the case where, as in some regions near the coast (especially in the west and south), calcareous formations, probably of tertiary age, have contributed to soil-formation. At some points there seem to exist phosphate deposits, well known elsewhere to occur in such rocks, which impart to the soils exceptionally high percentages of phosphoric acid, even exceeding one per cent. The phosphates of course remain practically untouched by the leaching processes, and appear to be somewhat widely diffused; so that the soils of Madagascar may be said to be, on the whole, well supplied with this important plant-food.
In the central province of Imerina the valleys and lower slopes show a fair content of both lime and potash; but in the province of Betsileo, adjoining it on the south, nearly every one of the soils analyzed is reported as containing only “traces” of lime, together with very small amounts of potash in most cases. The ultimate analyses of ignited red earths, of which an average is here given, are of interest in this connection.
ULTIMATE ANALYSIS OF
IMERINA RED SOILS, IGNITED;
AVERAGE OF THREE.
| Silica | 55.2 |
| Potash | .3 |
| Lime | trace |
| Magnesia | 1.1 |
| Ferric oxid | 10.6 |
It is quite obvious that only leaching-down and concentration of the feeble resources of such material in the valleys can produce soils worthy of permanent cultivation.
One point, however, is strikingly illustrated in several of the analyses given in the subjoined table. We find in the original quite a number of cases in which the field notes report considerable fertility, while the chemists’ judgment is very unfavorable. Thus we find recorded for the soil No. 267, taken near the village of Anjozorabe, in the Maintirano region, “luxuriant vegetation and remarkable crops,” with such minute proportions of potash, lime and phosphoric acid that the authors are compelled to say that the land offers “no cultural resources.” The same occurs in the cases of soils Nos. 370, 261, and several others having either “good crops” or “abundant natural vegetation.” Unless we assume that in these cases the samples were not properly taken, we are obliged to conclude that under the local climatic conditions, such minute amounts of plant-food are developed with sufficient rapidity to supply good growth. This would be quite parallel to the case of the tea soils of Assam, whose production lasted 30 years before showing exhaustion, on plant-food percentages only slightly greater than those here noted, and determined by a much more incisive method.
It is thus quite obvious that a different standard of interpretation must be applied to tropical soils as compared with either the temperate humid, or the arid regions; and that uniform methods of analysis are needed to evolve a definite rule from the present uncertainties.