Evaluation of Nitrate Accumulation and Factors Affecting It in Some Leafy Vegetables in Zanjan Province

Nitrogen (N) fertilizer plays an important role in crop yield and its quality. Excess nitrates may cause surface and groundwater pollution, through nitrate leaching and soil erosion. The uptake and distribution of nitrate in crops is important with respect to environmental concerns and the quality of crop products. This study was conducted in a randomized design at harvesting time on some vegetables such as Allium cepa L, Petroselinum crispum, vulgaris subsp, Anethum graveolens, Coriandrum sativum and Mentha Piperita in 7 fields in Zanjan Province. Concentration of nitrogen, nitrate, and activity of nitrate reductase enzyme in the vegetables as well as some physical and chemical properties of soil and water were determined. Results showed that, despite the same climatic conditions and crop management, the highest accumulation of nitrate was observed in samples of irrigation water, soil, and plants in the fields near the municipal sewage sludge outlet that were cultivated with leguminous plants i.e. beans and alfalfa, in previous years; therefore, no nitrogen fertilizer application was required. In all studied field, nitrate concentration in Allium cepa L and Petroselinum crispum was in critical range; however, nitrate concentration in 14.3% of vulgaris subsp and Mentha Piperita vegetable fields and 28.6% of Anethum graveolens and Coriandrum sativum vegetable fields were higher than critical range. Concentration of nitrate in vegetables had positive correlation with concentrations of plant nitrogen and water and soil nitrate content and had negative correlation with nitrate reductase activity. Also, significant differences were observed in nitrate reductase activity in various vegetables. Among the studied soil properties, soil nitrate concentration had an important role in nitrate accumulation in vegetables.