Potassium doses and frequency of application to alfalfa in a tropical soil
The objective of this study was to evaluate the effect of doses and frequency of application of potassium fertilizer on the alfalfa dry matter yield and potassium content in plant and soil. The experimental was carried out in a Typic Hapludox and was designed in randomized blocks in 4 X 4 factorial with 3 replications. The treatments were 4 levels of potassium in topdressing fertilization (0, 600, 1200 and 1800 kg ha-1 year-1 of K2O) and 4 frequency of application (12 = after each cutting, 6 = after two cuttings, 4 = after three cuttings; and 2 = two applications per year). The use of 1420 kg.ha-1 per year of K2O applied after two cuttings (6 applications per year) increased alfalfa dry matter yield until 30500 kg ha-1 and provided the best use of K at the higher doses of fertilizer. Alfalfa shoot total K removal reached 704 kg ha-1 per year of K2O with the application of 1623 kg ha-1 per year of K2O. At the end of the experiment, soil exchangeable K increased with K rates, and the differences were observed util 0.6 m of depth.