Ionic balance of sorghum in relation to pH, NO3-and NH4+in the nutrient solution
2000
Ali, N.A. | Mohamed, B.A. (Agricultural Research Corporation, Wad Medani (Sudan)) | Findenegg, G.R. (The Agricultural University, Wageningen (The Netherlands))
Sorghum (Sorghum bicolor (L) moench (var. Bogor) has been grown in nutrient solution with continuously controlled constant pH. Shoot samples have been analyzed for organic acid composition by gas liquid chromatography and for inorganic mineral composition. In order to evaluate the relative importance of the nitrogen form (NO3-NH4+) and external pH as factors influencing ionic balance, the effect of low pH (pH 3.7) during NO3- nutrition and that of NH4+ nutrition at pH 6.0 have been established separately in relation to the standard growth. Neither NH4+ nutrition nor low pH affected growth rates of the plants significantly. Low pH reduced the sum of all identified organic acids and the excess of inorganic cations over inorganic anions (C-A) by about 41% and 26%, respectively, compared to the control growth conditions. Trans-aconitic acid was the most important compound in compensation of C-A, both quantitatively and with respect to its close correlation to C-A values in plant samples receiving different treatments. In contrast, C-A and total organic acids were not much affected by NH4+ compared to NO3- at pH of 6.0. This was due to an increase in inorganic anion accumulation (SO4-H2PO4-) with NH4+ nutrition which balances the lack of NO3-accumulation of these plants nearly quantitatively. It is suggested that accumulation of inorganic anions might facilitate normal ionic balance and growth rate during NH4+ nutrition. Although the total organic acid content was affected by the form of nitrogen supplied, changes were observed in the relative contributions of individual acids
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