tUnder natural conditions, an experiment was carried out to investigate the impact of the recommendedand optimized doses of two herbicides on the biological properties of five soybean cultivars inoculatedwith Bradyrhizobium japonicum, grown in pots. The required dose of haloxyfop-P-methyl or imazethapyrwith adjuvant Adigor®in which 95% control of johnsongrass and velvetleaf was obtained (30.42 and50.69 g active ingredient ha−1, respectively) were chosen as the optimized doses to compare with theirrecommended doses (100 and 108 g active ingredient ha−1, respectively). In general, toxicity of the rec-ommended doses was higher than the optimized doses. In most biological properties of five soybeancultivars, haloxyfop-P-methyl was more toxic than imazethapyr, e.g. shoot dry weight, root nitrogencontent, and shoot phosphorus content. But, the intensity of these effects depended on type and concen-tration of herbicides, and soybean cultivars. In instance, at recommended dose of haloxyfop-P-methylor imazethapyr as compared with control, the nodule number was reduced up to 71%, 97%, 36%, and83% in Williams, Sari, Bt Tellar and Inter Price varieties for the former while those were reduced up to54%, 89%, 70%, and 93% for the latter, respectively. Clark variety was unaffected in this respect. Moreover,nodulation was unaffected with the optimized doses of herbicides.

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