Abstract
1. Vine growth, nutrient absorption and respiratory activity of fibrous roots as affected by both different nitrogen sources and controlled soil atmosphere were observed with two-year-old, non bearing Delaware grapes. Oxygen concentration in the soil atmosphere was controlled at six levels of 20 (air alone), 15, 10, 5, 2 and 0 (nitrogen gas alone) per cent respectively by mixing air with nitrogen gas. Sodium nitrate (NO3-N) and ammonium sulfate (NH4-N) were employed as nitrogen source and their effects on growth were compared in relation to the soil oxygen level.
2. Regardless of the soil oxygen concentration, average shoot length and total fresh weight of vines were always superior in the NH4-N than in the NO3-N treatment. The growth rate, however, was more depressed in the former than in the latter as the soil oxygen level decreased.
3. The total N concentration of leaves in the NO3-N treatment was nearly the same throughout the different soil oxygen levels, while that in the NH4-N treatment was lowered markedly as the soil oxygen level decreased less than 2 per cent. The P, K and Mg concentrations of leaves were depressed in the both treatments with decreasing soil oxygen level, though the trend with P and K was rather slight.
4. Respiratory activity of fibrous roots was measured with a Warburg′s manometer by soaking them in 0.1M solution of either sodium nitrate or ammonium sulfate. In general, the respiration rate was higher in the NO3-N than in the NH4-N treatment. When the oxygen concentration in the respiration chamber was changed from 20 to 0 per cent, the oxygen uptake and carbon dioxide evolution declined noticeably in both treatments. Particularly, the tendency was more marked in the NH4-N treatment, showing the higher R.Q. value than in the NO3-N treatment.
