Chemical composition, nitrate reductase activity and plastid pigments content in lucerne under the influence of ammonium and nitrate form mineral nitrogen
Institute of Forage Crops, 89 Gen. “Vladimir Vazov” Str., Pleven 5800, Bulgaria, E-mail: email@example.com
A pot trial was carried out at the Institute of Forage Crops, town of Pleven, Bulgaria (2003–04). Whereas ammonium and nitrate forms of mineral nitrogen are assimilated for the plants, the influence of these two forms of mineral nitrogen on the chemical composition, nitrate reductase activity and plastid pigments content of lucerne in conditions of optimum moisture and water deficiency stress was tested. Urea as a source of ammonium nitrogen and potassium nitrate as a source of nitrate nitrogen were used. Rates of 70, 140 and 210 mg N kg-1soil were applied. It was found that mineral nitrogen in ammonium form, applied at the doses of 140 and 210 mg N kg-1 soil at optimum moisture increased crude protein content by 5–13%, and in the nitrate form at the same doses, by 3–7%. Crude protein content under water deficiency stress increased by 4–21% for ammonium, and by 3–12% for the nitrate form of mineral nitrogen. When the plants were supplied insufficiently with nitrogen, water deficiency stress more strongly deteriorated the chemical composition of lucerne, crude protein decreased by 6% and crude fiber increased by 10%. The application of mineral nitrogen under optimum moisture decreased calcium and phosphorus content, and the decrease was bigger for the nitrate form (up to 10% for calcium, and 23% for phosphorus). Under water deficiency stress the content of calcium and phosphorus decreased, but there were no differences for two forms of mineral nitrogen. At the optimum moisture and water deficiency stress, there was a similar tendency to reduce nitrate reductase activity in leaves, when applied mineral nitrogen at a dose of 70 mg N kg-1 soil in both forms, and to increase at the doses of 140 and 210 mg N kg-1 soil. The total content of plastid pigments increased as compared to unfertilized control, when mineral nitrogen was applied in both forms.