---

Background & objectives: This study aimed to evaluate use of humic organic and chemical fertilizers to compare their effects on nitrate concentrations in potatoes from three main cultivated areas of Ardabil suburbs.
Methods: Potatoes were cultured in one hectare land in each suburban villages; Great Arallow, Small Arallow, Pyraqum and Jabedar. 0.5 hectare of the each land was fed by conventional chemical fertilizer and the remaining with natural humic fertilizer. Potatoes were randomly harvested and transferred to the laboratory from each part. Sample preparation and nitrate quantification were done based on Jones method using a spectrophotometer at 410 nm wavelength, respectively.
Results: Comparison of total average nitrate in potato tubers showed that nitrate levels in the fields feding by humic fertilizer (i.e. 88.5 mg/kg) was lower than the levels quantified in potatoes fed by chemical fertilizers (with total average nitrate of 112.6 mg/kg); 38  mg/kg decline in nitrate levels.
Conclusion: Comparing to chemical (conventional) fertilizers, application of organic fertilizer is effective to reduce nitrate levels of potato tubers. Therefore, using this fertilizer in agriculture industries can be considered in long-term programs of fisheries organizations to reduce adverse effects.