ABSTRACT
Agricultural intensification to increase corn yield has increased the demand for nitrogen fertilizers. A field experiment was carried out in Candói, Paraná State, Brazil, on a clayey Typic Hapludox (Oxisol) under a long-term continuous no-till (30 years) to evaluate the effects of nitrogen (N) fertilization as urea in top dressing on soil acidification and determine the N-urea rates of maximum technical yield (MTY) and maximum economic yield (MEY) for obtaining high corn yield. A randomized complete block design was used, with four replications. The treatments consisted of N-urea application in top dressing at the rates of 0, 90, 180, 270, and 360 kg∙ha-1. Urea was applied in the V4 stage of the crop corn. Corn, hybrid P1630, was cultivated after black oat in 2012, with 65 kg N∙ha-1 at sowing. The N application as urea decreased the soil pHCaCl2, the exchangeable Ca2+ + Mg2+ levels, the effective cation-exchange capacity (CEC) and the soil base saturation. The N content in leaves and grains, the plant and ear height, the number of grains per row, the mass of grains per ear, the 1,000-grain mass, and the N export by grain of corn increased linearly with increasing N rate applied in top dressing. Corn yield increased with N rates as the Linear Response Plateau model and stabilized at 19.6 t∙ha-1. The MTY and MEY would be obtained at a rate of 209 kg N∙ha-1 in top dressing.
Key words:
Zea mays L.; nitrogen; urea; nutrition; high yield
