Abstract

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.

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