LAUSR

Abstract Supplementation of Na in reduced amounts can eliminate K deficiency through the partial substitution K+ by Na+, reducing pasture fertilization costs. This replacement requires adjustments considering the crop, since high levels of exposure to Na correlate negatively with the absorption and transport of phosphorus to the leaves by the plants. Therefore, this study aimed to evaluate the effects of phosphate sources associated with the partial replacement of K+ by Na+ in Mombasa grass (Megathyrsus maximus). The experiment was carried out under greenhouse conditions using a completely randomized experimental design with three replications. A total of twelve treatments were obtained in a 3 × 4 factorial scheme, represented by three sources of phosphorus: simple superphosphate, natural phosphate and UFT-fertil organic compound and for four doses of Na+ (NaCl) in order to replace the recommended dose of K+ (80 mg dm−3): 0 + 80, 20 + 60, 40 + 40 and 60 + 20 mg dm−3 of Na+ + K+, respectively. Overall, superphosphate showed the lowest values for sodium adsorption ratio, percentage of exchangeable Na+ and its contents in the soil. There was no reduction in the productivity of Mombasa grass due to the partial replacement of K+ by Na+ when using superphosphate.