الفهرس 
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Abstract
the application of herbicides into the soil is accompanied by several proplemes . such as accumulation in the soil and inhibition of the benificial activities of soil micro-organisme , e.g.,the symbiotic and non symbiotic fixation of atmospheric nitrogen. Thus the aim of the present study was to gain some information about the effect of pre-emergence application of some herbicides at different rates on nodulation , nitrogen fixation and growth of soybean plants on soil respiration and on non-symbiotic nitrogen fixation in the soil.