Fosfato natural reativo aplicado em épocas distintas e associado a fertilizantes nitrogenados afetam a produção de capim-marandu

The objective of this study was to evaluate the ideal time of application of reactive natural phosphate combined with nitrogen fertilizers for Marandu grass fertilization. The experiment was conducted in a greenhouse using a random block design with six treatments and six replicates. A 3x2 factorial scheme consisting of three times of application of reactive natural phosphate (before, together and after liming) and two nitrogen sources (ammonium sulfate and urea) was used. No interaction was observed between the time of reactive natural phosphate application and nitrogen fertilizer. However, in the first cut, reactive natural phosphate resulted in a larger number of leaves and tillers (47 leaves/pot and 13 tillers/pot) when applied after liming and increased leaf blade mass (4.26 g/pot) when applied together with liming. In the second and third cut, the time of application did not influence any of the variables studied, except for residual dry matter which was lower (20.17 g/pot) when reactive natural phosphate was applied before liming. Treatment with ammonium sulfate resulted in a lower pH in the three cuts performed. In the second and third cut, a higher leaf blade dry mass (12.5 and 14.8 g/pot, respectively) and a larger number of leaves (95 and 111 leaves/pot, respectively) and tillers (29 and 39 tillers/pot, respectively) were observed for the treatment with ammonium sulfate. The time of application of reactive natural phosphate exerted no significant effect on the agronomic efficiency of the three cuts. However, in the third cut, the application of reactive natural phosphate together with or after liming was superior to the soluble phosphate source. Reactive natural phosphate should be applied together with or after liming, regardless of the nitrogen fertilizer used. Ammonium sulfate optimizes the development of Marandu grass after regrowth of this forage.