Mombasa grass is being widely cultivated due to its productive potential, broad adaptability, high quality and ease of establishment. However, this forage is considered demanding and requires medium to high fertility soils. Given the above, the present work aimed to evaluate the production and morphogenesis of Megathyrsus maximus Jacq grass. cv. Mombaça as a function of nitrogen and phosphate fertilization on cerrado soil, as well as to evaluate the efficiency and utilization rates of nitrogen. The experiment was conducted in a greenhouse under a completely randomized design with six replications. The 20 treatments were obtained in a 2 x 2 x 5 factorial scheme, comprising two fixed doses of phosphorus (100 and 246 kg P2O5 ha-1), two nitrogen sources (Source 1: 23-00-00 + 0.4 Mg + 9.3 Ca + 10.5 S and Source 2: 23-00-00 + 0.5 Mg + 9.0 Ca + 10.3 S) and five doses of N each source (0, 50, 70, 90 and 110 kg N ha-1). Mombasa grass was grown in Red yellow Latosol dystrophic manure corrected previously. Nitrogen fertilization, regardless of the source, provided positive and promising results for the agronomic characteristics and physiological indices of Mombaça grass under both phosphorus conditions. Among the tested phosphorus conditions, we found that the application of 100 kg P2O5 ha-1 was more efficient in increasing the evaluated characteristics, being the most indicated in the production system of Mombaça grass. The average nitrogen dose, regardless of source, that provided the best results was 100 kg N ha-1 under the condition of 100 kg P2O5 ha-1. Doses above 100 kg N ha-1 promoted a reduction in nitrogen utilization efficiency in the recovery of nitrogen applied by Mombaça grass, but obtained a higher agronomic efficiency.
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