Performance of a soybean–maize off-season double crop system in response to potassium fertilization strategies in a Brazilian Cerrado oxisol

ABSTRACT Soybean–maize cropping system is widely used in the Brazilian Cerrado region. A field experiment was performed in a Cerrado oxisol to evaluate potassium (K) fertilization strategies on the performance of a soybean–maize cropping system. Five fertilization treatments were investigated, including control (unfertilized), KCl, polyhalite, KCl + polyhalite (72/28, % based on K), and KCl + lime + gypsum. In all K fertilization strategies, a rate of 66.5 kg K·ha-1 was applied only at the time of soybean sowing. Soybean and maize grain yields were not significantly influenced by K fertilization management, but the cumulative grain yield of the cropping system (soybean + maize) was 21% higher by using polyhalite than KCl. Exclusive fertilization with polyhalite resulted in higher export of K by soybean grains. In addition, it was the only treatment capable of providing a positive magnesium (Mg) balance in the soybean–maize cropping system (+2.51 kg·ha-1). The calcium (Ca) and sulfur (S) balance was positive under the use of polyhalite, KCl + polyhalite, and KCl + lime + gypsum. Fertilization with polyhalite proved to be an excellent strategy to improve the performance of a soybean–maize cropping system by increasing the cumulative grain yield and providing a positive balance of Ca, Mg, and S.