Nitrogen and potassium fertilization of Marandu grass

Nitrogen and potassium are among the nutrients most extracted by forage grasses, making it essential to identify the appropriate doses for efficient fertilization planning. Therefore, this study aimed to determine the maximum nitrogen dose to be supplied for the fertilization of Marandu grass and to assess whether potassium supplementation increases the efficiency of nitrogen fertilization. The experiment was conducted at the Experimental Farm of the Federal University of Mato Grosso, which is located in the municipality of Santo Antônio do Leverger. A completely randomized design was used, with 10 treatments arranged in a 5×2 factorial scheme, with 3 replications. The treatments consisted of five nitrogen doses (0, 25, 50, 75, and 100 kg N ha⁻¹) and two potassium doses (0 and 25 kg K₂O ha-1) applied after each defoliation cycle. The fertilizers used were ammonium sulfate and potassium chloride. The variables analyzed were forage mass, percentage of leaf blades, stem + sheath, tiller population density, ground cover, forage participation, and biomass of invasive plants. Nitrogen fertilization increased the forage mass, modified the morphological composition, and led to tillering. Potassium increased only the forage mass. There was an increase in the forage mass and accumulation rate up to a nitrogen dose of 50 kg ha-1 per cycle. Using nitrogen doses higher than these resulted in losses and may cause luxury consumption, which only increases production costs. Nitrogen also increased tiller population density, which is important for preventing degradation processes and extending pasture longevity, as it provides greater ground cover and prevents erosion and the emergence of invasive plants. For this reason, nitrogen doses from 50 kg ha⁻¹ completely suppressed the emergence of invasive plants. Combining the potassium dose (K₂O) of 25 kg ha⁻¹ with the absence of potassium fertilization revealed increases in forage accumulation of 10%, 12%, and 18% when associated with nitrogen doses of 0, 25, and 50 kg ha-1, respectively. Therefore, potassium fertilization clearly increases the efficiency of nitrogen fertilization; however, an economic viability assessment should be conducted for the rational use of this fertilizer. The maximum nitrogen dose per defoliation cycle is recommended to be 50 kg ha⁻¹ for Marandu grass