Potassium leaching from black oat ( Avena strigosa [ Avena nuda]) and pearl millet ( Pennisetum glaucum) straw as affected by simulated rainfall at different times after chemical desiccation was evaluated. Cover crops were grown in pots, in Botucatu, Sao Paulo, Brazil. Fifty days after emergence, the plants were sprayed with herbicide. The straw received simulated rains corresponding to 5 and 10 mm, considering a mulch of 8 t/ha, 3, 6, 9 and 15 days after desiccation. The amount of K leached from the plant residues increased after desiccation. Fifteen days after desiccation, a rainfall of 10 mm leached 11.1 kg/ha of K. A higher potential of black oat straw to leach K was observed with 10 mm of rain. The amount of K released by rains from black oat straw was greater than the pearl millet with 5 and 10 mm of rain, and this difference increased according to water loss from tissues.
