It will be observed that the figures of this table differ materially only in the matter of potash from those given in [chapter 19, p. 354]; for the latter substance they would have to be multiplied by from 2 to 4, according to the lime-content and other conditions.
With this understanding a number of Wohltmann’s analyses of soils from Samoa and Kamerun are given below, the potash determinations made with hot acid being placed in parentheses after the other.
Soils of Samoan Islands.—A discussion of these analyses shows, from the writer’s point of view, a very low content of potash and lime, with the peculiarity that both are somewhat higher at the depth of a meter than in the surface ten-inches. This is probably to be accounted for from the very high content of organic matter (humus), which is apparent from the high “loss by ignition,” a very large proportion of which must be credited to the burning of the organic matter. That this humus reaches to the lowest depths examined, is clear from the nitrogen-content given for these samples. Wohltmann, whose estimate of these soils agrees in most respects with the writer’s, attributed to them a very satisfactory nitrogen-content. This would be true of the total; but as he has not determined either the true humus or its nitrogen-content, it remains uncertain whether or not a sufficiency is in an available form, and whether their case may not be like that of the Hawaiian soil mentioned above ([chapter 19, p. 362]), in which despite 10% of humus and .17% of nitrogen, the land was found to be nitrogen-hungry. Again, as regards the phosphoric acid, which Wohltmann considers satisfactory to high, it is questionable to what extent it is rendered unavailable by the very high content of ferric hydrate. We are thus left in some uncertainty as to the real manurial requirements of the Samoan soils, which doubtless represent very closely also those of Tutuila, the chief American island of the group.
ANALYSES OF TROPICAL SOILS
BY F. WOHLTMANN.
Extraction with cold chlorhydric acid,
sp. g. 1.15, for 48 hours.
- (A) = Tuanaimato. Virgin Forest Soil, not given.
- (B) = Le Utu Sao Vaa Cultivated Soil.
- (C) = 0—25 cm. (10 ins.)
- (D) = 75—100 cm. (30—40 ins.)
| SAMOAN ISLANDS. | |||||
|---|---|---|---|---|---|
| Upolu. | Savaii. | ||||
| (A) | (B) | Cleared Land. | |||
| Depth. | (C) | (D) | (C) | (D) | |
| Potash[152] | .05 | .048 | .022 | .063 | .036 |
| (.07) | (.077) | (.043) | (.102) | (.043) | |
| Lime | .07 | .113 | .033 | .042 | .023 |
| Magnesia | .37 | .285 | .144 | .067 | .074 |
| Ferric Oxid | 21.53 | 17.600 | 19.653 | 15.333 | 18.733 |
| Alumina | 12.40 | 9.621 | 11.217 | 18.941 | 16.413 |
| Silica | .99 | 2.043 | 2.853 | .366 | 1.250 |
| Titanic Acid | |||||
| Phosphoric Acid | .30 | .179 | .213 | 29.096 | .187 |
| Org. Matter and Water | 18.49[153] | 17.288 | 12.770 | 29.146 | 16.332 |
| Nitrogen in Soil | .30 | .447 | .186 | .697 | .128 |
| Hygr. Moisture | 6.80 | 15.062 | 13.242 | 15.288 | 12.862 |
| KAMERUN. | ||||
|---|---|---|---|---|
| Isongo. | Mundame II. | |||
| Depth. | (C) | (D) | (C) | (D) |
| Potash[154] | .097 | .104 | .076 | .110 |
| (.101) | (.163) | (.123) | (.168) | |
| Lime | .193 | .154 | .150 | .125 |
| Magnesia | .283 | 1.415 | .198 | .099 |
| Ferric Oxid | 7.305 | 7.497 | 13.920 | 11.707 |
| Alumina | 14.298 | 14.504 | 5.223 | 5.531 |
| Silica | .047 | .108 | .227 | .120 |
| Titanic Acid | ||||
| Phosphoric Acid | .064 | .224 | .131 | .205 |
| Org. Matter and Water | 23.335 | 12.299 | 10.154 | 9.549 |
| Nitrogen in Soil | .187 | .079 | .164 | .103 |
| Hygr. Moisture | 20.065 | 15.329 | 14.811 | 16.498 |
It is probable that for crops requiring so much potash as do the banana and cacao trees, potash is the first need when they cease to produce well on these soils.
Soils of Kamerun.—In the soils of Kamerun, also analyzed by Wohltmann, and of which two are placed alongside of those of Samoa, it is at once seen that the materials from which they have been formed are richer in both potash and lime than the parent rocks of the Samoan, and not quite so rich in iron. They are also very rich in organic matter, evidently down to the depth of a meter, as are those of Samoa. It is probably due to the high humus-content that these soils, washed as they have been by the second-highest rainfall in the world (about 35 feet annually) have not been as thoroughly leached as have been those of the Brahmaputra valley. The annual rainfall of Samoa is only from nine to eleven feet on the lower levels, but ranges as high as 18 feet at higher elevations.