FACTORS OF SOIL FORMATION - Midlands State University

that driven off above 110°C, also speaks for significant chemical and
physical conversions of rock into soil.
Hardy (7) has reported a significant accumulation of nitrogen and
organic matter on recent volcanic-ash soils of the Soufrière district in
St. Vincent, British West Indies. Fourteen years after the last volcanic
eruption, the surface foot layer of soils at an altitude of 2,000 ft.
contained 0.022 to 0.035 per cent nitrogen and 1.0 to 2.0 per cent
organic matter. In 1933, 30 years after the eruption, the reforested
region had attained comparative stability. Surface-soil samples
collected at 10 different sites showed an average organic-matter
content of 2.1 per cent and an average nitrogen content of 0.10 per
cent (carbon-nitrogen ratio = 12.2) in the upper six-inch layer, values
that are comparable with those for most of the cultivated soils of St.
Vincent. "Thus," writes Hardy, "within 10 to 20 years, sterile volcanic
ash may give rise to fertile soil under the prevailing circumstances."
TABLE 8.—CONDENSED DATA OP A LANG-EILAND SOIL, 45 YEARS OLD
(Van Baren, et al.)
Annual rainfall = 262 cm. (103 in.)
Annual temperature = 27.8°C. (82°F.)
Middle Surface
Constituents Rock layer soil
SiO 2 , per cent 67.55 65.87 61.13
Al 2 O 3 , per cent 15.19 16.31 17.24
Fe 2 O 3 , per cent. 1.52 1.74 2.56
FeO, per cent 2.15 2.05 2.59
CaO, per cent 2.89 3.07 3.61
Na 2 O, per cent 4.47 4.01 3.90
K 2 O, per cent 1.95 1.53 1.78
CO 2 , per cent — — 0.04
H 2 O, above 110°, per cent 2.46 3.17 3.25
H 2 O, below 110°, per cent 0.04 0.33 1.53
Organic matter, per cent — — 0.45
Nitrogen, per cent 0.018 0.012 0.035
pH 5.3 5.8 6.0
Particles below 20µ, per cent — 22.4 26.1
Color White White Gray
SiO 2 :Al 2 O 3 = sa 7.56 6.86 6.03
β (see p. 27) — 0.816 0.776
Soil-time Relationships on Recent Moraines.—Since the
absolute movements of a number of alpine glaciers during the last
hundred years are fairly accurately known, the study of their moraines
provides good quantitative data on rates of soil formation. Figure 18
illustrates the relative positions of the Mittelberg Glacier in Tirol and
two terminal moraines that were deposited in 1850 and 1890. Miss
Schreckenthal (16), in 1935, studied a number of soils in this region
(Table 9). In spite of seemingly unfavorable climatic conditions,
particularly low temperatures, the moraines have been significantly
altered within a period of 80 years. Soil acidity developed rapidly, silt
became relatively abundant, and even some clay was formed.
Notwithstanding the paucity of the flora, soil nitrogen is now high.
Hoffmann (16), working in the same vicinity, reports nitrogen
analyses that are presented in graphic form in Fig. 19. The nitrogentime
curve appears to ascend in logarithmic manner, tending to
approach a maximum. Although the data are quite scanty, they
demonstrate, nevertheless, the rapid accumulation of soil nitrogen at
high altitudes.