Effects of Calcium Application and Air Flow on the Growth and Inorganic Content in Allium fistulosum L. under Excess Ammonium Nitrogen.

For nitrate nitrogen reduction, Japanese bunching onion (Allium fistulosum L.) cvs. 'Kincho' and'Yakko'were cultivated in a nutrient solution in which nitrate nitrogen was wholly replaced by ammonium nitrogen. The softening of the root by ammonium nitrogen nutrition significantly decreased under gentle air flow. The occurrence of leaf tip withering was negatively correlated with the Ca content in the leaf blade of 'Kincho' which is comparatively resistant to the high ammonium nitrogen, and it was reduced by Ca application and/or air flow. On the contrary, in 'Yakko', a cultivar sensitive to the high ammonium nitrogen, there was no correlation, and there was no reduction effect by Ca application and/or air flow. In 'Yakko', excess salt concentration in the nutrient solution by the Ca addition increases the physiological disorder, and the growth was better at Ca 1 meL-1 which is lower than the standard concentration of 2 meL-1. The fact that even in the plants without nitrate nitrogen nutrition contained nitrate nitrogen in the leaf sheath and blade about the same level as usual plants, suggests nitrification occurs considerably in this soilless culture. Growing management according to the cultivar may be necessary for the increase of the ratio of ammonium nitrogen to nitrate nitrogen, which is commonly done before the harvest for quality improvement.