Efficiency of phonolite as a potassium source for Paiaguás palisadegrass

ABSTRACT Potassium chloride (KCl) is the most widely used potassium source to meet crops requirements. However, Brazil’s dependence on imports to meet the national demand demonstrates the need to assess the efficiency of other sources of this nutrient. The present study aimed to assess the agronomic efficiency of phonolite in natura and its mixture with a water-soluble source (KCl), for Paiaguás palisadegrass. The experiment was conducted in a greenhouse, with a sandy clay loam typic Hapludox. A completely randomized block design was used, in a 3 x 5 factorial scheme, consisting of three K sources (KCl, phonolite and a 30 % of KCl + 70 % of phonolite blend) and five doses of the nutrient (0, 50, 100, 150 and 200 mg kg-1), with four replications. The phonolite doses promoted a linear increase in the dry weight production, albeit inferior to KCl for all the cuttings, whereas the KCl (30 %) and phonolite (70 %) blend showed a better fertilization efficiency than phonolite alone, which exhibited an intermediate effect. The agronomic efficiency was 29 % for the phonolite alone and 63 % for the blend, and the critical K levels in the soil and shoots were, respectively, 1.4 mmolc dm-3 and 8.7 g kg-1.