Effect of Nitrogen Fertilization and Season of Growth on Nitrate Content of Spinach Plants (Spinacia oleracea, L.)

Abstract A pot experiment was carried out in two seasons, winter and spring, using three nitrogen sources, ammonium sulphate, calcium nitrate and urea, in five rates of application, 0,25,50, 100 and 150mg N/Kg soil. Spring sown spinach outyielded the winter plants and accumulated higher amounts of N. Winter plants contained more protein. Source of N had no effect on yield or the plants content of any of the studied N‐fractions. The first N‐dose increased the yield over the control. Protein and water soluble N content increased with the successive N‐additions up to 100 mg N/Kg soil. Most of the soluble‐N was accumulated in spinach in the nitrate form. The first N‐dose increased NO, % to 3 fold over the control. The nitrate content increased also with every yield increment. Petioles contained higher amounts of nitrate than leaf blades. There was a linear relationship between total and nitrate‐N.