An earlier application of potassium fertilizer, in the cultivation of cover crop species preceding the main summer crop in no-tillage system can be an advantageous in commercial farming. This study evaluated grain yield and K accumulation in soyabean due to an earlier application of potassium fertilizer to a pearl millet cover crop, and compared to K applied at sowing of the subsequent soyabean under no-tillage. The experiment was conducted in Sao Paulo, Brazil during the 2000/2001, 2001/2002 and 2002/2003 growing seasons, on a dystroferric red Latosol (sandy loam Oxisol), cultivated with soyabean (summer) in rotation with black oats (winter) under no-till for two years prior to the experiment. Pearl millet ( Pennisetum glaucum) was sown in September over the residues of black oat ( Avena strigosa [ Avena nuda]), and soyabean ( Glycine max) was planted in the first weeks of December, in the three growing seasons. The treatments consisted of 0, 30, 60, and 90 kg/ha K 2O doses applied to pearl millet, in combination with 0, 30, 60, and 90 kg/ha K 2O applied to soyabean. Soyabean plants were harvested 25, 50, 75, and 100 days after emergence, and the grains harvested at the end of the experiment in order to determine K accumulation and yield. The early application of 60 to 90 kg/ha K 2O at pearl millet sowing did not affect K accumulation in soyabean plants. Soyabean yields were higher with applications of 80 to 90 kg/ha K 2O, which can be totally applied at pearl millet sowing. The anticipation of the application of KCl at pearl millet sowing reduced K export in soyabean grains.
