The aim of this study was to compare the effects on plant growth of the main mixed N forms containing urea with that of nitrate and nitrate-ammonium as an N source for two plant species, wheat (tolerant to ammonium) and Capsicum (sensitive to ammonium). The experiment was performed in a growth chamber and plants were grown in siliceous sand pots. Capsicum plants received only one level of N: 8,5 mmol/L, whereas wheat plants received three levels of N: 2, 8,5 and 15 mmol/L. Treatment compositions for 8,5 mmol/L are described in Table 1.
Table 1. Composition of treatment solutions for a N level of 8,5 mmol/L. All concentrations are in mmol/L.
Results showed that for both wheat and Capsicum the growth of plants, fed with mixed nitrogen forms containing urea, was similar to that of plants receiving nitrate and nitrate/ammonium. Only for Capsicum, fed with ammonium/urea a significant decrease in plant growth was found (Table 2).The presence of nitrate (as for example supplied with KNO3) corrected the negative effects of ammonium and urea nutrition on the growth parameters of Capsicum plants.
Table 2. Effects of different nitrogen forms on growth parameters of Capsicum plants.