68
WALLACE H. FULLER
(Shuvalov, 1966). This is due to the roots of the shrublike desert plants
not spreading out in the upper horizons which dry out rapidly but growing
more uniformly deep.
The brown Sierozem soils have more organic matter than the Graybrowns and a C to N ratio in the order of 6-9.5 (Rozanov, 1951). Red
desert soils of Arizona rarely accumulate more than 1.0% organic matter
except in the thin surface (0-2.5-cm layer) near established vegetation.
Winds redistribute fallen leaves, scale and plant parts which collect around
stationary objects.
The conclusion (Rozanov, 1951) reached with respect to the quantitative nature of central Asian desert soils is that the relatively very low
humus content is chiefly due to the activity of a highly biogenic soil process, and not, as previously supposed, to a low amount of vegetative
remains entering the soil. In a virgin Sierozem of Central Asia the total
reserve of root residues were found to be 2.13 kg/m
2
and the humus 4.9
kg/m
2
. Most of the roots were concentrated in the 0-7-cm layer
(Kononova, 1961). The amount of plant growth above the ground, and
of root substance in certain desert soils are compared with the more humid
soils (Rozanov, 1951) in Table II.
In the B horizon of desert soil profiles, iron-containing minerals may
yield iron to soil-forming processes. The fixation of F e O 3 and FeO in situ
by repeated wetting and drying and microbial activity into molecules of
soil organic acids is reported by Ponomareva (1956).
The presence of a significant amount of organic phosphorus compounds
in desert soils has been established (Fuller and McGeorge, 1950b) (see
Fig. 13). The organic ratio of P to C is lower in desert soils than in most
soils of the humid climates.
TABLE I I
A COMPARISON OF THE PLANT MATERTAL ABOVE AND B E L O W GROUND LEVEL
AMONG FIVE D E S E R T SOILS AND F O U R M O R E H U M I D SOILS OF CENTRAL ASIA"
Plant
Plant
tops
roots
Soil
(metric tons/ha)
Sandy sierozem
0.5
10.0
Light-gray sierozem
1.0
15.0
Light-gray sierozem
0 . 5 - 1 . 5
21.4
Ordinary sierozem
2 . 1 - 4 . 5
—
Dark sierozem
4 . 5
30.0
Plant
Plant
tops
roots
Soil
(metric tons/ha)
Light chestnut
0 . 8 - 1 . 5
—
Dark chestnut
5.2
13.2
Southern chernozem
7.0
25.0
Carbonate chernozem
—
25.8
a Data obtained from Rozanov, 1951, Table 91, p. 342.
WALLACE H. FULLER
(Shuvalov, 1966). This is due to the roots of the shrublike desert plants
not spreading out in the upper horizons which dry out rapidly but growing
more uniformly deep.
The brown Sierozem soils have more organic matter than the Graybrowns and a C to N ratio in the order of 6-9.5 (Rozanov, 1951). Red
desert soils of Arizona rarely accumulate more than 1.0% organic matter
except in the thin surface (0-2.5-cm layer) near established vegetation.
Winds redistribute fallen leaves, scale and plant parts which collect around
stationary objects.
The conclusion (Rozanov, 1951) reached with respect to the quantitative nature of central Asian desert soils is that the relatively very low
humus content is chiefly due to the activity of a highly biogenic soil process, and not, as previously supposed, to a low amount of vegetative
remains entering the soil. In a virgin Sierozem of Central Asia the total
reserve of root residues were found to be 2.13 kg/m
2
and the humus 4.9
kg/m
2
. Most of the roots were concentrated in the 0-7-cm layer
(Kononova, 1961). The amount of plant growth above the ground, and
of root substance in certain desert soils are compared with the more humid
soils (Rozanov, 1951) in Table II.
In the B horizon of desert soil profiles, iron-containing minerals may
yield iron to soil-forming processes. The fixation of F e O 3 and FeO in situ
by repeated wetting and drying and microbial activity into molecules of
soil organic acids is reported by Ponomareva (1956).
The presence of a significant amount of organic phosphorus compounds
in desert soils has been established (Fuller and McGeorge, 1950b) (see
Fig. 13). The organic ratio of P to C is lower in desert soils than in most
soils of the humid climates.
TABLE I I
A COMPARISON OF THE PLANT MATERTAL ABOVE AND B E L O W GROUND LEVEL
AMONG FIVE D E S E R T SOILS AND F O U R M O R E H U M I D SOILS OF CENTRAL ASIA"
Plant
Plant
tops
roots
Soil
(metric tons/ha)
Sandy sierozem
0.5
10.0
Light-gray sierozem
1.0
15.0
Light-gray sierozem
0 . 5 - 1 . 5
21.4
Ordinary sierozem
2 . 1 - 4 . 5
—
Dark sierozem
4 . 5
30.0
Plant
Plant
tops
roots
Soil
(metric tons/ha)
Light chestnut
0 . 8 - 1 . 5
—
Dark chestnut
5.2
13.2
Southern chernozem
7.0
25.0
Carbonate chernozem
—
25.8
a Data obtained from Rozanov, 1951, Table 91, p. 342.