الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
Soybean {Glycine max (L) Merr.} is an important leguminous crop all over the world. Because of its high concentration of protein (36%), oil (18%), and carbohydrate (20%), it is grown in almost all parts of the world for human consumption, industry and animal feed (Boydak et al., 2002). Soybean is considered by many agencies, including the US food and drug administration, to be a source of complete protein that contains significant amount of all the essential amino acids that must be provided to human body because of the body’s inability to synthesize them. In addition , soybean may be grown as vegetable which has a sweet and nutty flavour and rich in protein, fat, phosphorus, calcium, iron, vitamins B1 and B2, and has the highest net protein utilization value of all soybean products. It is harvested and sold as fresh or frozen pods or shelled beans. Therefore, efforts are being focused on increasing the productivity of soybean crop by growing high yielding cultivars under the most favourable agricultural conditions.
Because of increased industrial and municipal demand for fresh water supplies, preserving fresh water sources plays a crucial role in sustainable agriculture. Increasing demand for fresh water sources makes it necessary to save as much water as possible. Since agriculture alone uses about 80–90% of fresh water sources (Walker, 1989), there is much stress on agricultural water users to use efficient irrigation systems and/or considered deficit irrigation practices (Lamm et al., 1993). Therefore, researchers have been studying possible effect of reduced irrigation practices especially on crop yield parameters. Depending on the hybrid, soybean growth period ranges usually between 90 to 120 days and requires 450–700mm of water (Doorenbus and Kassam, 1979). The most critical period for water stress in soybean was claimed by some researchers to be the flowering stage and those stages following flowering.
The sustainability of any crop production system depends on maintaining adequate soil plant nutrient levels. Nitrogen is an essential plant nutrient and, in agriculture, fertilization with nitrogen products is widely and increasingly practiced to increase the production yield of food (Reinhold- Hurek and Hurek, 2003). . Nitrogen nutrition in soybean is met by a combination of the uptake and assimilation of inorganic−soil N and symbiotic N2 fixation. The relative importance of these two sources of N in meeting the crop’s N needs changes depending upon the availability of inorganic −soil N. Thus, when inorganic −soil N is abundant, N2 fixation is inhibited or delayed and the proportion of N in the crop derived from N2 fixation is decreased. Conversely, when there is little inorganic −soil N available, N2 fixation provides the majority of the crop’s N needs. The proportion of soybean crop’s N derived from inorganic −soil N or from N2 fixation may also change depending upon whether or not the crop is exposed to drought or other environmental constraints.. However, the use of elevated doses of fertilizers, as well as pesticides, may have negative and unpredictable effects on the environment, and contribute to the contamination of soil, water and natural areas.