The primary metabolites, very abundant in nature, are essential for the physiological development of the plant; they are present in large quantities, they are easy to extract, and their exploitation is relatively cheap. In order to establish mathematical expressions that relate the regrowth age with the nitrogen and sugar content (glucose, fructose and sucrose) of the whole plant and its fractions. The experiment was developed, following a randomized block design, with 5 treatments (60, 90, 120, 150 and 180 d). In the first part of this communication the content of Nitrogen (N) in the integral plant, leaves and stems were evaluated. In the second part we studied sugars like Glu, Frut and Suc. Reporting that N, Glu, Frut and Suc decreased with the highest results at 60 days and quadratic and cubic equations with R2 higher than 0.90 were adjusted. The established regression equations explain the close relationship between regrowth age and the contents of precursor metabolites (N, Glu, Frut and Suc), which explains the fluctuations found in sugars influenced by the phenological state of the plants and photosynthetic activity of this. Insert abstract text here.