Nitrogen Use Efficiency and Its Components of Maize in Different Environments.

In the temperate areas of Argentina, maize crops were traditionally sown at early spring (September-October) with warm temperatures. After the appearance of transgenic maize hybrids resistant to Lepidoptera, the late sowed maize crops (December to mid-January) have spread and vegetative period is exposed to high air temperatures which not only affect crop growth but also soil nutrient dynamics. The aim of this work was to evaluate N use efficiency (NUE; in kg grain per unit of available N) and its components: N utilization efficiency (NutE; in kg grain per unit N uptake) and N uptake efficiency (NupE; in kg N uptake per unit available N) of maize crops in contrasting environments (location x sowing dates). Field experiments were conducted at two locations: Pergamino (Lat. 33.9°S) and Paraná (Lat. 31.8°S). At each location, treatments included a combination of two sowing dates (SD), three N rates (0, 90 and 270 kg N ha^-1) and four hybrids (DK66-10VT3PRO, DK70-10VT3PRO, DK72-10VT3PRO, DK73-10VT3PRO). In both locations, NUE differed among hybrids (P<0.05) and was linearly reduced by N rate (P<0.001), but with a different slope among SD and locations. Hybrid DK73-10VT3PRO had the lowest NUE reduction by N rate. More than 68% of NUE variations were accounted (P<0.0001) by NupE variations. NupE differed among hybrids (P<0.001), was reduced as N rate was increased and was higher in early than in late SD only in Paraná. NutE of DK70-10VT3PRO and DK73-10VT3PRO was consistently higher (P<0.002) across locations and SD and was decreased as NupE was increased only in Paraná. The superior performance of DK73-10VT3PRO was explained by its lower NUE sensitivity to high N rates.