ABSTRACT

The physicochemical properties of arid soils do not favor the abundant fixation of humus in the USSR (Kononova, 1961). The rapid cycle of the formation and decomposition microbial process, in the short periods when soil moisture is available, accounts for the accumulation of substances of the fUlvic acid type. The very rapid rate of decomposition of plant residues in the Sonoran Desert soils of North America is also reported to result in narrow G!N ratios, ranging from 8 to 10 in the upper few centimeters compared with ratios of 10-12 in the more humid soils in the Midwest prairies of the United States (Fuller, 1975a). Even in small amounts, though, organic matter exerts a profound influence on the physical and biological characteristics of the soil. The maintenance of this small amount is essential for maximal plant growth.