In an effort to improve fertility, recover degraded areas and increase support for the capacity of livestock on pasture, new forms of fertilizer are being developed. Polymer-coated monoammonium phosphate (MAP) is an innovative source of phosphorus (P) for maintaining forage grass productivity. The aim this study was to evaluate the agronomic efficiency of P rates with the presence and absence of the polymer on the productivity, development and nutritional value of hybrid signalgrass (Urochloa spp.) cv. Mavuno. The field research was conducted on a dystrophic Ultisol. The experiment was arranged in a randomized complete block design with four replications and treatments applied in a factorial scheme (2 × 4) + 1. The treatments included two P sources (uncoated MAP and polymers-coated MAP) at four rates (20, 40, 80 and 160 kg ha−1 of P2O5), and the control received no P fertilization. The measured variables showed no differences between sources with or without polymer. The maximum production of accumulated shoot dry weight yield (SDWY) of the ‘Mavuno’ grass was 20.2 Mg ha−1 with the dose of 114 kg ha−1 of P2O5. The value of crude protein and in vitro dry matter digestibility showed a quadratic response with maximum production of 76.5% and 15.9% for the P2O5 rates of 37.2 and 91.1 kg ha−1, respectively, while the acid detergent insoluble fiber showed a linear increase up to the rate of 80 kg ha−1 of P2O5. No differences were observed in plant height, number of tillers, or the relative chlorophyll content between treatments.