Doses and potassium partitioning methods in soybean production components in an Amazonian savanna

After nitrogen, potassium is the macronutrient most required by soybean. To meet soy bean growth demands, it is necessary to use high K doses, which can lead to losses via leaching. The objective of the current study was to evaluate the effect of doses and methods of K fertilization on the components of soybean production, in the Yellow Latosol of an Amazonian savanna. The experiment was conducted using randomized complete block design with four replicates. Plots consisted of two fertilization methods (M1 – fertilization on planting and at 35 days after emergence - DAE and M2 – on planting, then divided between 20 and 35 DAE). Subplots where five doses of potassium (K2O at 0, 40, 80, 120 and 160 kg ha-1) were randomized. Measured variables were: plant stand (PS), plant height (PH), height of first pod insertion (FP), number of pods per plant (PP), bean mass per plant (BM), and bean yield (BY). Because of the low exchangeable K content and medium texture of the study soil, deployed methodology consisting of plant fertilization and two applications to facilitate high soybean yields. Agronomic efficiency proved to be a good indicator for assaying the best K2O dose, as it is sensitive to initial soil exchangeable K levels. The dose giving maximum agronomic efficiency was 88.5 kg ha-1 of K2O, converting each kg of K2O in 14.3 kg of soybeans.