Rice is classified as an ammonium (NH4+)- tolerant plant due the predominance of this ion in flooded soils. However, in the oxygenated zones of flooded soil and in the rice rhizosphere, nitrate (NO3-) can be formed and become an important nitrogen (N) source for the crop. This experiment was carried out to evaluate the effect of different ammonium:nitrate proportions on rice development in nutrient solution. The experiment was carried out in a greenhouse, from January until February 2008 in a nutrient solution with the following NH4+: NO3- proportions: 100:0, 75:25; 50:50; 25:75 and 0:100, at 5.0 mmol L-1 N. The genotype IRGA 417 was used and the biomass production, the nitrogen, calcium, magnesium and potassium contents in tissue and xylem sap were evaluated. The presence of ammonium at the proportions 100:0 and 75:25 resulted in plant toxicity, as well as for nitrate at the proportions 25:75 and 0:100. The combined supply of ammonium and nitrate increased biomass production in relation to solely NH4+ or NO3- supply. Ammonium in solution affected negatively Ca and Mg, whereas no effect was observed on N or K tissue contents. However, in the xylem sap, both K, Ca and Mg contents were affected by ammonium. The higher total absorbed quantities of N, K, Ca, and Mg and better rice development indicated that the combined supply results in higher nutrient absorption efficiency than solely ammonium or nitrate supply.
nitrogen; toxicity; Oryza sativa L; nitrification
