Kafkafi, U., Hebrew University of Jerusalem, Dept. Fld. Crops, Vegetables Genet., Faculty of Agriculture, Rehovot, 76100, Israel
Ganmore-Neumann, R., Institute of Soil and Water, Volcani Center, P.O. Box 6, Bet Dagan, Israel

Tissue analysis of plant material is used to estimate the level of sufficiency or deficiency of any particular nutrient. Published values of ammonium-ammonia reported in plant cell extracts would have been toxic to plants, if these values are really present in the cell. We believe that the ammonia determined in plant tissue is actually ammonium produced by the decomposition of soluble amino compounds in the plant tissue during the extraction or analytical procedure. Therefore, pure amino acid solutions and water extracts of wheat (Trticum aestivum L) and melon (Cucumis melo L) leaves were examined by several analytical procedures for nitrate-nitrogen (N-NO3) and ammonium-nitrogen (N-NH4). The results showed that glycine, alanine, glutamic acid, and methaionine released more than 7% of its nitrogen (N) as ammonium during the auto analyzer procedure. Water extracts of melon leaves from plants grown in ammonium solution exhibited more ammonium than those of plants grown in nitrate alone. Wheat grown in high N-fertilized plots, released more N-NH4 in the distillation of their leaf water extracts than plants grown in low N- fertilized plots. The N-NH, content decreased with plant age and with a decrease in total N concentration. It is concluded that ammonium determined in water extracts of plant material is a result amino acid breakdown during the analytical procedure. The values depend on plant age and the composition of its amino acids, analytical method employed, distillation time, pH and temperature during the reaction time.