NITROGEN INFLUENCE ON DOUBLE-CROPPED CORN YIELD AFTER SOYBEAN

To evaluate the influence of topdressed nitrogen application time (stages 1, 2, and 3) and sources (urea, ammonium sulfate, and Entec® + control), on double-cropped corn yield after soybean, the experiment was conducted at Ivani Farm, Santa Carmem, Mato Grosso State, Brazil (12°00'S, 55°14'W, altitude 365 m), in the 2008 growing season. The treatments were arranged in a randomized complete block design, as a 3x4 factorial scheme (time of application x source of nitrogen), with four replications. The source x time interaction was not significant for any of the characters measured, indicating that these factors were independent. The application at stage 3 (ten expanded leaves) provided the greatest spike diameter, length of grain, rows of grains per spike, and grain yield, while spike length, cob diameter, prolificacy, and weight of hundred grains were not affected by times of N application. Regarding N sources, they only affected spike length, cob diameter, and grain yield, as compared to control. No significant differences were observed among N sources. Nitrogen application influenced positively the corn performance double-cropped after soybean. KEY-WORDS: Zea mays L.; urea; ammonium sulfate; ammonium sulfonitrate; nitrogen fertilizing; no-tillage.