Agronomic performance of soybean doses and time of application of potassium in Piauí Savanna

Abstract

The fertilization is influenced by the specific climatic conditions of each region, and, for some regions, there is not a recommendation to potassium fertilization for soybean by the official research bodies, such as the state of Piaui. The objective of this study was to evaluate the efficiency of doses and time of application of potassium (K) in soybean in Piauí Savanna. The field work was conducted in dystrophic Oxisol. The experimental design was a randomized complete block design with four replications in a factorial (5 × 4) + 1, and the treatments consisted of combinations of five doses of potassium: 30, 60, 90, 120 and 150 kg ha-1 (K2O ) + control (zero kg ha-1) applied in four seasons: 100% at planting; 50% at planting and 50% at 30 days after sowing (DAS); 100% at 30 DAS; 50% to 20% at 50 DAS and 40 DAS. We evaluated the following variables: height and dry weight of plants; leaf chlorophyll content and K; agronomic efficiency in the use and recovery of K; grain harvest index, and productivity. Only agronomic efficiency in the use and recovery of K was influenced by the times of application of K. With the exception of dry matter and the relative chlorophyll content, all other variables were significantly influenced by K rates applied. Also became the exception agronomic efficiency in the use of K, which showed an exponential decrease with increasing doses. The application of 90 kg ha-1 K2O gave greater increases in other variables.