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. The objective of this study was to evaluate grain yield and K accumulation in soybean due to an earlier application of potassium fertilizer to a pear millet cover crop, and compared to K applied at sowing of the subsequent soybean under no-tillage. The experiment was conducted at the Faculdade de Ciências Agronômicas - Universidade Estadual Paulista, Botucatu, state of São Paulo, in the 2000/2001, 2001/2002 and 2002/2003 growing seasons, on a Dystroferric Red Latosol (sandy loam Oxisol), cultivated with soybean (summer) in rotation with black oats (winter) under no-till for two years prior to the experiment. Pear millet (Pennisetum glaucum) was sown in September over the residues of black oat (Avena strigosa), and soybean (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-1 K2O doses applied to pear millet, in combination with 0, 30, 60, and 90 kg ha-1 K2O applied to soybean. The experiment was in random blocks, using a 4 x 4 factorial design with four replications. Soybean 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-1 K2O at pear millet sowing did not affect K accumulation in soybean plants. Soybean yields were higher with applications of 80 to 90 kg ha-1 K2O, which can be totally applied at pear millet sowing. The anticipation of the application of KCl at pear millet sowing reduced K export in soybean grains.
Glycine max L. (Merrill); early fertilization; potassium chloride; cover crop
