The use of coated fertilizers and the concept of the critical N dilution curve are alternatives capable of improving the production efficiency of wheat (Triticum aestivum L.) crops in agro-ecosystems. The objectives of this work were to evaluate the effect of a slow release urea-coated fertilizer on (i) the production of wheat's shoot biomass at the anthesis stage, (ii) the concentration of N in the shoot biomass, and (iii) the N availability in the Andisol. Two fertilizers: urea and urea-coated were evaluated using four increasing N rates and a control treatment (without fertilization), in three application strategies, during two growing seasons (late sowing [S1] and early sowing [S2]). Samples of shoot biomass and soil (0–20-cm depths) were collected at five wheat growth stages (Z21, Z31, Z39, Z45, Z69 on the Zadoks scale). The average production of shoot biomass was 10.3 t dry matter (DM) ha–1 for S2 and 7.9 t DM ha–1 for S1 and N concentrations was between 1.0–3.0%. When using a coated urea fertilizer in this Valdivian agro-ecosystem, no statistical differences (P <.05) in shoot biomass or wheat N concentrations were found at anthesis (Z69). Differences were principally between seasons. We therefore proposed a new adjustment to the dilution N curve, with a value concentration critical, Nc start of 3.80%, and 4.15%, for S1 and S2, respectively. Use demand parameters such as Nc adjusted to the agro-ecosystem for wheat crop, allows to rationalize the fertilization according to inorganic N available from the soil.