POLIHALITA COMO FONTE DE POTÁSSIO PARA ADUBAÇÃO DE SOQUEIRA DE CANA-DE-AÇÚCAR

Abstract

Polyhalite is a mineral source of potassium (K) and other nutrients, which can be used as fertilizer for crop production. The tested hypotheses were i.) polyhalite can be an alternative fertilizer to potassium chloride (KCl) for sugarcane, with the advantage of providing, in addition to K, also Ca, Mg and S, and ii.) the lower solubility of polyhalite associated with multiple nutrient composition can provide a residual effect in soil. In this scenario, polyhalite was evaluated in comparison to KCl, in the potassium fertilization of the fourth and fifth ratoon of sugarcane (variety CTC 4). The experiment was carried out in October 2019, in the field, in the municipality of Jataí, GO, Brazil, in a dystrophic Red Latosol. The experimental design was randomized blocks, with four treatments and five replicates. The treatments consisted of a control treatment without potassium fertilization, and the K sources, applied in isolation (KCl and polyhalite) or in combination (blend of polyhalite + KCl in the proportion 25/75, respectively). The ratoon fertilizations were carried out based on the replacement of 1.3 kg ha-1 of K2O for each ton of stalks produced in the previous harvest. In Chapter I, it was observed that potassium fertilization in the ratoon, regardless of the K source, increased the sugarcane stalks production in the first year and in the sum of the years. It was also observed that the combination of polyhalite + KCl (blend) conferred greater plant height compared to the treatment without potassium fertilization; and that when comparing the isolated K sources, fertilization with polyhalite provided greater stalk diameter and higher leaf S content. These results most likely occur due to the multiple nutrient composition of polyhalite, reinforcing the potential of the source to be an alternative to KCl in sugarcane fertilization. The experiment results in Chapter II indicated that polyhalite presented the highest K contents in the 0-20 cm layer after two sugarcane cultivation cycles. For S content, the differences between the fertilizers were more evident, with treatments containing polyhalite presenting the highest S contents up to 40 cm in depth. The gradual release of the nutrients contained in polyhalite indicates a residual effect in the soil, which may be beneficial for sugarcane crops in subsequent crops and thus be an alternative to the KCl use.