Potassium leaching from plant cover straw at different senescence stages after chemical desiccation

Chemical control of green cover crops is common in no-till systems and nutrient mineralization of the residues left on the soil surface can be intensified by rainfall over time after the plant desiccation. Potassium leaching from six green cover crops was evaluated as affected by rainfall simulated at different stages after the herbicide application. Pearl millet (Pennisetum glaucum), guinea sorghum (Sorghum vulgare), black oat (Avena strigosa), triticale (Triticum secale), Indian hemp (Crotalaria juncea), and brachiaria (Brachiaria decumbens) were grown under greenhouse conditions in pots with soil in Botucatu, Sao Paulo, Brazil. The plants were sprayed with non-selective post-emergence herbicide fifty days after emergence. After the desiccation (2, 4, 8, and 16 days) the plants were cut and subjected to 30 mm of simulated rainfall, simulating an amount of 8 t ha(-1) of straw. The amount of K leached from the straw increased as plants died off after herbicide application. Regarding the K supply to the subsequent crop, triticale straw was the best alternative, as it made over 9 kg ha(-1) of K until 16 days after herbicide application available.