root temperature, concentration and the ratio no3-/NH4+ effect on plant development

The effect of ammoniumion in the solution on plant growth and ionic composition is reviewed.It is demonstrated that ammonium is taken up in preference to nitrate when its concentration is above 10 % of total nitrogen in the nutrient solution. Ammonium is a safe source at low root temperatures, and is dangerous at high temperatures. Sensitivity of crops to ammonium varies between species. Chinese cabbage may die in the presence of 5 mM ammonium but thrives on 0.05 mM. The response of various crops to various ratios of ammonium in the solution leads to the conclusion that the rate of sugar supply to the roots minus the demand for root respiration is the key factor that controls the ability of the plant to assimilate ammonium in the root.