EFFECTS OF THE RATE AND FORMS OF APPLIED NITROGEN IN NURSERY SOILS ON SEEDLING GROWTH OF DIFFERENT VEGETABLE SPECIES

The dynamics and balance sheet of applied nitrogen were studied to ascertain the optimum application rate and forms of N for vegetable production in nursery soils. The results are summarized as follows: 1. The best performance of seedlings was obtained with 250 mg Nitrogen.liter-1 of nursery soil (mg N.liter-1) for cucumber, melon, watermelon and tomato, and 500 mg N.liter-1 for eggplant and pimento. 2. Rates of 500 mg N.liter-1 and over caused a significant reduction in the growth of cucumber, melon and pimento seedlings, but less significantly for watermelon, tomato and eggplant. 3. A good performance of the seedlings was obtained when 50 to 100 mg N.liter-1 was applied in a nitrate form. At these levels, the nitrogen concentration in saturation extracts of nursery soils was maintained about 200 ppm N throughout the period of the experiments. 4. Seedlings which performed well absorbed 25 to 50% of the applied N. Approximately 10 to 25% of the N was retained in the soil; 45 to 50% of the applied N was unaccounted for and may have leached out from the root zone. 5. The rate of nitrogen loss due to leaching was fastest during the first week of the experiment. The rate decreased thereafter. It was concluded that for most vegetable crops, the optimum range of nitrogen application to nursery soils lies between 200 to 300 mg N.liter-1 of which 50 to 100 mg is recommended to be applied initially in the nitrate form.