II. DESERT SOILS
67
be severe for crops of the Coonamble Downs Desert region (Riceman,
1953). Molydenum deficiency appears to be associated with P deficiency
in Australian soils. Manganese deficiencies are found in varying degrees
in calcareous aeolian sand, Terra Rossas, solidized-Solonetz, and calcareous gray soils. Rozanov (1951) reports that soils of Central Asia are sufficiently supplied with "microelements."
Iron and zinc deficiencies are reported for scattered areas in Washington, Oregon, California, Arizona, New Mexico, and other western states.
Iron deficiencies were observed by the author in some desert soils of South
America.
F. ORGANIC MATTER
Organic matter content and composition in soils has received considerable attention because of its disproportionately favorable effect on
chemical, physical, microbiological, and morphological properties of soil as
compared with the mineral matter. Moreover soil organic matter is the nitrogen carrier. The rather narrow range of C to N ratios indicates the direct
relationship of N with organic matter and the almost complete dependency
of N fertility in virgin soils on organic matter. Soil organic matter consists
of partially rotted residues of the plants that occupied the land and materials formed by soil organisms. Soil organic matter is not derived wholly
from plants. Soil organisms make a substantial if not dominant
contribution.
The accumulation of humus is low in desert soils compared with those
of other climates, but the plant-ash residues, mainly carbonates, are higher.
The organic matter of desert U.S.S.R. soils, for example, are reported
(Ponomareva, 1956) to be intensely mineralized. She emphasizes the importance of the soil biology and humus on desert soil formation as exemplified by her statement: "The mineral forms of biogenic carbon and
generally plant ash compounds shape the profile and properties of desert
soils" (Ponomareva, 1956, p. 34).
The content of total humus in gray-brown desert soils of Central Asia
ranges from 0.3 to 0.8% and seldom exceeds 1.0% (Lobova, 1960),
whereas the total nitrogen varies from 0.03 to 0.3%. The Gray-brown
desert soils have a low C to N ratio, 3-5, indicating extensive decomposition. Fulvic acids are proportionately higher, being two or three times as
abundant in these highly mineralized soils as in other soils. Waxes and
resins ("bitumens") are also proportionately high among arid soils. Desert
plants, the source of organic residues, are abundantly supplied with waxes,
resins, and essential oils. In the drier desert soils, the humus content is
small and is distributed fairly uniformly throughout the soil profile
67
be severe for crops of the Coonamble Downs Desert region (Riceman,
1953). Molydenum deficiency appears to be associated with P deficiency
in Australian soils. Manganese deficiencies are found in varying degrees
in calcareous aeolian sand, Terra Rossas, solidized-Solonetz, and calcareous gray soils. Rozanov (1951) reports that soils of Central Asia are sufficiently supplied with "microelements."
Iron and zinc deficiencies are reported for scattered areas in Washington, Oregon, California, Arizona, New Mexico, and other western states.
Iron deficiencies were observed by the author in some desert soils of South
America.
F. ORGANIC MATTER
Organic matter content and composition in soils has received considerable attention because of its disproportionately favorable effect on
chemical, physical, microbiological, and morphological properties of soil as
compared with the mineral matter. Moreover soil organic matter is the nitrogen carrier. The rather narrow range of C to N ratios indicates the direct
relationship of N with organic matter and the almost complete dependency
of N fertility in virgin soils on organic matter. Soil organic matter consists
of partially rotted residues of the plants that occupied the land and materials formed by soil organisms. Soil organic matter is not derived wholly
from plants. Soil organisms make a substantial if not dominant
contribution.
The accumulation of humus is low in desert soils compared with those
of other climates, but the plant-ash residues, mainly carbonates, are higher.
The organic matter of desert U.S.S.R. soils, for example, are reported
(Ponomareva, 1956) to be intensely mineralized. She emphasizes the importance of the soil biology and humus on desert soil formation as exemplified by her statement: "The mineral forms of biogenic carbon and
generally plant ash compounds shape the profile and properties of desert
soils" (Ponomareva, 1956, p. 34).
The content of total humus in gray-brown desert soils of Central Asia
ranges from 0.3 to 0.8% and seldom exceeds 1.0% (Lobova, 1960),
whereas the total nitrogen varies from 0.03 to 0.3%. The Gray-brown
desert soils have a low C to N ratio, 3-5, indicating extensive decomposition. Fulvic acids are proportionately higher, being two or three times as
abundant in these highly mineralized soils as in other soils. Waxes and
resins ("bitumens") are also proportionately high among arid soils. Desert
plants, the source of organic residues, are abundantly supplied with waxes,
resins, and essential oils. In the drier desert soils, the humus content is
small and is distributed fairly uniformly throughout the soil profile