Desenvolvimento fenológico e agr？nomico de três híbridos de milho em três épocas de semeadura

variations in environmental conditions determined by different sowing dates have a great influence on maize ontogeny. this experiment was carried out to evaluate the phenological development of three maize hybrids, at three sowing dates. the experiment was carried out at the depress？o central region of the state of rio grande do sul-brazil during 2000/2001 grows season. the single-cross very early hybrid pioneer 32r21, the single-cross early hybrid dekalb 214, and the double-cross normal hybrid agroceres 1051 were evaluated at 08/22/2000 (early), 10/31/2000 (intermediate) and at 01/25/2001 (delayed) sowing dates, with no supplemental irrigation. all hybrids presented shorter developmental subperiods when sowing was delayed. tassel and ear differentiation occurred, respectively, in the stages of 6 to 7 and 10 to 11 completely expanded leaves, regardless of hybrid cycle and sowing date. the highest leaf emission rate occurred when very early hybrid was sown in october. delaying sowing resulted in a reduction of leaf area per plant mainly in early hybrids. number of spikelets per ear, grain yield and grain weight were generally higher in october than in the other two sowing dates.