Investigation on Soil Nitrate Pollution and Nitrate Accumulation in Potato and Tomato of Farmers’ Fields in Mashhad Plain

Water and nitrogen are two important factors that affect yield and plant growth. Excessive use of chemical fertilizers in recent decades, especially nitrogen fertilizer, has caused to nitrate pollution in soil, water and environment. This study was carried out to investigate the effects of different amounts of water and nitrogen fertilizers on the accumulation of nitrate in soil, tomato and potato plants. Research was performed on farms of Mashhad plain. Selected farms included 15 tomato and 15 potatoes fields. Irrigation method in all fields was furrow irrigation. During the growing season, the amount of water and nitrogen were measured in all fields. At the beginning and end of the growing season, the amount of nitrate in the soil (two depths of zero to 30 and 30 to 60 cm) and at the end of the growing season, the content of nitrate in both potato and tomato crops were measured. The measurement method was spectrophotometry (spectroscopy) at 540 nm. Results showed that the amount of water and fertilizer consumed in potato fields were higher than required. But, in tomato fields, water consumption was more than the required amount and, in some fields, the fertilizer was higher, and in some less than the recommended amount. With increasing water, nitrate decreased in two depth 0-30 and 60-30 cm whereas with the increase in fertilizer urea, soil residual nitrate increased at the end of the season. With increase in fertilizer application, nitrate residue in the plants increased. Thus, effects of excessive water on nitrate leaching and creating environmental problems are serious. To avoid such problems, crops water requirement must be estimated with great care. Also, fertilizer application should be balanced and in accordance with the type of plant and its yield.‎