Aspects of microbial activities and dinitrogen fixation in Egyptian desert soils

Rhizobium -Legume Symbiosis and Nitrogen Fixation under Severe Conditions and in an Arid Climate

“…The whole country forms part of the great desert belt that stretches from the Atlantic across the whole of North Africa through Arabia (366). An extremely arid climate prevails in Egypt; the high temperature, low relative humidity, high evaporation, and scanty rainfall (1.4 to 5.3 mm/year) all contribute to the fact that the greater part of Egypt is barren and desolate desert (3,366). The desert lands also include saline areas; saline lands represent about 15% of the arid and semiarid lands of the world (281,358).…”

“…Plant productivity in many arid regions is often limited by low soil fertility; therefore, the nutrient content of the soil should be considered in conjunction with the amount of moisture when selecting plants for deserts (3,300). One of the suggested treatments for building up the fertility of desert soils in Egypt is by application of a mixture of Nile sediments (clay) and organic manure; however, this suggestion was considered a nonpractical solution to improve the fertility of desert soils (3), since the huge amount of sediments required for the amelioration of large areas is not available.…”

“…BNF in deserts is mediated mainly by some heterotrophic bacteria, associative bacteria, cyanobacteria, actinorhizal plants, and legumes. The N 2 fixed by heterotrophic free-living bacteria is of minor importance as a mechanism for N input in arid soils (3,361). Associative dinitrogen-fixing bacteria may be potentially important in supplying relatively small amounts of N to associated grasses in arid lands (346).…”

“…. It is therefore necessary that the plant be able to detect the presence and level of NO 3 Ϫ in the rooting medium and to adjust its N 2 fixation accordingly. Symbiotic N 2 fixation in field legumes takes place against a changing background of mineral N availability as a consequence of mineralization, leaching, and, often, fertilizer application (81).…”

Persistence of twoRhizobium etli inoculant strains in clay and silty loam soils

“…Arid lands in Egypt represent about 96% of the total area of the country, where dry climate prevails. The high temperature, low relative humidity, high evaporation, and scanty rainfall (1.4 to 5.3 mm/year) all contribute to the fact that the greater part of Egypt is barren (ABDEL-GHAFFAR 1989). The limited acreage of agricultural land makes the intensive agriculture the only reliable approach to produce food and fiber for the increasing population in Nile Delta and Valley (ZAHRAN 1999).…”