It is well known that there is a greater demand for food due to a larger global population. To cope with this situation, the conventional agriculture uses various strategies, being the most important the use of nitrogen-based fertilizers. However, the inappropriate and excessive use of these fertilizers leads to the appearance of serious environmental problems such as the pollution of aquifers or the eutrophication of lakes and reservoirs.

In order to solve this problem, several studies have been conducted in various crops searching the optimization of the use of these fertilizers, in order to guarantee high crop yields in a sustainable way. In our work, we determine the optimal amount of nitrogen for the rootstock citrus crops (Citrus macrophylla) grown in controlled temperature and light conditions. The reduction to 50% of nitrogen content was studied through the analysis of several phenotypic (number of leaves, leaf area and fresh weight of roots) and biochemical parameters (total proteins and enzymatic activities of nitrogen-fixing enzymes such as nitrate reductase and nitrite reductase). Data obtained showed that there were no significant differences between plants grown under conditions of 100% of nitrogen content and plants grown with 50% of nitrogen content in all the analysed parameters, except that plants grown with 50% of nitrogen content showed less leaf area than plants grown with 100% of nitrogen content. This suggests that roots of C. macrophylla plants are able to develop, transport and assimilate nitrogen with half nitrogen fertilization.