The effect of the ammonium:: nitrate nitrogen ratio, total nitrogen, salinity (NaCl) and calcium on the oxalate levels of Tetragonia tetragonioides Pallas. Kunz.

There is oxalate present in the edible leaves of Tetragonia tetragonioides. We conducted four trials, to test individually the effects of the nitrate to ammonium nitrogen ratio, total nitrogen level, NaCl salinity and Ca level on the yield and oxalate levels of hydroponically grown T tetragonioides. The results of all four trials confirm that oxalate concentration is directly related to the ontogenetic stage of T. tetragonioides, with young plants having higher oxalate levels. The nitrate to ammonium nitrogen ratio had significant effects on oxalate, with lowest concentrations in plants grown in the 50% NO3-N: 50% NH4-N and 0% NO3-H: 100% NH4-N solutions (6.5%). However, plants grown in 0% NO3-N: 100% NH4-N had significantly lower fresh weights than those grown in the 100% NO3-N: 0% NH4-N and 97% NO3-N: 3% NH4-N treatments. Tetragonia tetragonioides grown in total nitrogen levels of 2.1, 5.4, 10.7, 17.8 and 35.7 mM (as nitrate) showed no significant differences in oxalate levels. Plants grown in 2.1 and 5.4 mM N had significantly lower fresh and dry weights, leaf numbers and leaf areas than those in all other treatments. Calcium levels had a significant effect on oxalate levels, with 1.6 mM Ca producing plants with significantly higher oxalate levels (12.5%) than 0.3 mM (11.8%) and 10 mM Ca (11.3%). Calcium levels had no significant effect on the growth of T. tetragonioides. NaCl salinity had a significant effect on oxalate content, with 850 mM NaCl producing a lower oxalate level (9.8%) than all other treatments. NaCl salinity also had a significant effect on growth, with growth parameters of plants in 100 mM NaCl significantly higher than for all other treatments, including the control of 0 mM.