This explains why plants can be grown and harvested from the same plot year after year without the need for man to replace the nitrogen that is continuously removed by harvested crops (Stewart, 1966). In this case, most of the nitrogen used by plants enters the soil via fixation of atmospheric nitrogen by soil microorganisms. The agri- cultural soils of the Tigris and Euphrates valleys located in Iraq are examples of such agricultural practices. tillage, Even after centuries of these soils continue to yield crops, and their perpetual fertility can be largely attributed to nitrogen fixation and to the conversion of soil minerals into soluble forms by soil microorganisms (Chandra et al., 1962). Desert areas in temperate zones of the North American continent have been defined as regions “of hot daytime summer temperatures, higher than average evaporation rates, and .. . less than ten inches of precipitation annually'' (Wheeler, 1971); consequently, they are envisioned by many people as barren wastelands. The newcomer to desert areas of the western United States may be surprised to see lush vegetation generated by seasonal precipitation in the higher elevations. Even in this arid climate, the existence of a viable plant community depends on microbial activities in soil to provide the plants with nitrogen from the atmosphere and with other inorganic plant nutrients. Thus, a "sterile desert," microbiologically speaking, is a misnomer because fungi and bacteria are present even in extremely arid soils of the Atacama desert of Chile, an area which is nearly devoid of vegetation (Cameron, 1969). Nitrogen fixation has been reported for certain soil bacteria (Alexander, 1961) and for certain fungal strains of Aspergillus, Mucors, Penicil~ium, and Botrytis (Waksman, 1927; Griffin, 1972; Alexander, One of these nitrogen-fixers, Aspergillus, 1961). is the most prevalent fungus in some of the Iraqi soils mentioned earlier, as determined by microbial analyses (Chandra et al., 1962); this fungus was also found in different soil types of the Nevada Test Site Shields, 1960; Au, (NTS) (Durrell and 1974). It was reported earlier that plutonium when added as soluble and insoluble compounds to culture media was absorbed by Aspergillus 68