الفهرس 
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Abstract
1-Introduction
Mineral elements which stimulate growth and development of plants, but are not essential for their existence or those essential only for certain plant species or under specific conditions , are usually defined as beneficial elements ;this term applies in particular to sodium and cobalt .Marking the distinction between beneficial and essential elements is specially difficult in case of some trace elements.
Development in analytical chemistry and methods of minimizing contamination during biological studies may lead, in the future, to an increase in the list of essential elements and corresponding decrease in the list of beneficial ones.
Cobalt is also an essential constituent of vitamin B12 which is considered to be the only cobalt containing compound yet found in the human body. Cobalt is an essential element for the synthesis of vitamin B12 which is required for plant, animal and human nutrition.
Food crops (quantitively & qualitatively) are affecting the National Security World-Wide. In developing nations food represents the major item in family, society and national budget. Food prices are subsidized by the government (60%). Annual population in Egypt affects positively the gap of food sufficiency. Egypt being a developing country, suffers from gap between production and consumption. There is no doubt that increasing the productivity of food crops in the developing countries, such as Egypt, is the main goal to overcome the gap in food sufficiency resulting from the high annual increase in population.
The import of about 893 thousand tons (oil gab 93% in Egypt ) of edible oils is the average annual increase.
Egypt national plan include expansion of land reclamation until (2025) in the sandy, saline and desert soils. Water resources are the major obstacle in this target. Cobalt is considered a border element for plant nutrition. It is proved to be beneficial for higher plants such as tomato, cucumber and olive, in spite of the absence of evidence direct role in their metabolism. Cobalt is an essential element for legumes because of its use by micro-organisms in fixing atmospheric nitrogen. Cobalt is the central atom of vitamin B12.Cobalt is an essential element for the synthesis of vitamin B12 which is essential for the nitrogen fixing bacteria and it has been identified in root nodules of leguminous plants.