Productivity and Yield Components of Soybeans under Dose and Potassium Application Period in Piaui Savannah

The objective of this study was to evaluate the efficiency of rates and application periods of K on soybeans in the Savannah in Piauí. The work was carried out in a dystrophic oxisol. The experimental design was randomized blocks with four replications in a factorial design, the treatments consisted of combinations of five potassium doses 30, 60, 90, 120 and 150 kg ha-1 (K2O) + witness (0 kg ha-1), applied at four different times: 100% at soybean sowing, 50% at sowing and 50% at 30 days after sowing (DAS), 100% at 30 DAS, 50% at 20 DAS and 50% to 40 DAS. Evaluated the following variables: height soybean plants, dry biomass, internal efficiency in the use of nutrient-K (IENU-K), number of pods per plant-1, number of grains per pod-1, a thousand seeds weight, grain harvest index and productivity. There was no effect concerning the period of application of K in the variables analyzed. Exceptions done for dry biomass and the number of pods per plant-1, the other variables were significantly influenced by K rates. All variables significantly influenced by the application of K rates showed quadratic response, in which, exception of IENU-K, the curves showed the highest values by applying 83 to 93 kg ha-1 K2O.