ISHS Acta Horticulturae 807: International Symposium on Strategies Towards Sustainability of Protected Cultivation in Mild Winter Climate
ROOT ZONE TEMPERATURE AND THE PREFERRED FORM OF NITROGEN TO CROPS |
| Author: | U. Kafkafi |
| Keywords: | ammonium, nitrate, root sugar content |
| DOI: | 10.17660/ActaHortic.2009.807.44 |
| Abstract:
Nitrate, Ammonium and Urea are used in intensive glasshouse crop production. Season and daily temperature fluctuations are observed in glasshouse crop production. The sensitivity of crops to the presence of urea or ammonium in the root zone depends on: 1- temperature of the root. 2- Rate and amount of sugar flow from the leaves to the roots. The ammonium N is metabolized in the root cells and produces NH3 (ammonia) that require the presence of sugar to neutralize it. The sugar in the cell is used for binding ammonia in the production of glutamate or glutamine. When sugar in the cell is depleted due to excess respiration or shortage of light, ammonia reacts as a respiration poison and the cell dies in few seconds. There are differences between plants in their sensitivity to the concentration of ammonium in the nutrient solution. Corn, rice, and sorghum, are not sensitive to the presence of ammonium in the root zone up to 5 mM N-NH4 in the solution, while tomato, lettuce, Chinese cabbage, and spinach, are very sensitive. In strawberries the sugar content in the root decreased with the increase of root temperature until root death was observed at 32 °C. Root temperature of potted plants, (when not controlled in glasshouse production), might quickly rise during the day. Fine roots are the first to die due to ammonium toxicity. Root temperature and external concentration of ammonium in the solution are the major factors in determining the plant sensitivity to the form of N fertilizer in the root media. The implications of this mechanism on the type of fertilizer selection in glasshouse crop production will be discussed. | |
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