Nitrogen fertilizer use by citrus trees is affected by varying nitrate and ammonium ratios

Nitrogen (N) fertilization in citrus orchards is prone to significant environmental losses. Managing nutrients for sustainable development and optimizing nitrogen use efficiency (NUE) are key tasks in modern agriculture. NUE depends on N uptake and assimilation. In addition to intrinsic fertilizer use efficiency, we evaluated plant growth, nitrate reductase (NRase) activity, and the nutritional status of citrus plants fertilized with different N sources [calcium nitrate (CN), ammonium nitrate (AN), and ammonium sulfate (AS)]. After 240 days, plants supplied with either CN or AN exhibited higher biomass production and N accumulation in the leaves than those fertilized with AS. The supply of ammonium-containing sources (AN and AS) reduced the substrate pH, in which those with AS exhibited lower N partitioning to the leaves, as well as reduced the absorption and accumulation of magnesium and phosphorus. NRase activity was higher in plants supplied with CN or AN compared to AS, and CN fertilization provided the greatest NUE. The data demonstrated that citrus plants fertilized with sources containing nitrate increased the NUE from 10 to 25% and consequently had greater growth compared to those fed with AS.