Estratégias de manejo da urochloa brizantha cv. marandu submetida a diferentes doses de nitrogênio e frequências de corte

Abstract

Nitrogen acts directly on the growth and development of forage plants. Management recommendations based on the number of leaves expanded per tiller indicates a favorable alternative to guide defoliation management. The objective of this study was to evaluate the best Marandu grass management strategy (Urochloa brizantha cv. Marandu) as a function of defoliation management, based on the time for the appearance of two, three or four expanded leaves per tiller and on two levels of nitrogen fertilization. (90kg N ha-1 ) and (180kg N ha-1 ) in the period from November 22, 2018 to April 30, 2019. The treatments were distributed in a completely randomized design under a 2x3 factorial arrangement (90 and 180kg N ha-1 x 2.3 and 4 leaves emerged by tiller) with six treatments and three replications, totaling 18 experimental units. The response variables were total dry matter, leaf blade dry matter, stem and dead material, tiller population density and leaf: stem ratio. The protocol used for the evaluations was carried out when the average of nine tillers reached the expected number of leaves 2,3 and 4 leaves emerged, making the cut after collecting 50% of the plant based on the average height of the canopy in each experimental unit. The productive and structural characteristics were estimated with the data. The grass responded with different growth rates between minimum and maximum fertilization. The height of the canopy increased with the appearance of new leaves, with 33.4; 36.5 and 41.3 cm for 2; 3 and 4 leaves, respectively, responding to expectations. Tiller population density (DPP) and stem dry mass (MSC) showed higher values in the treatments of two and three leaves, not differing statistically between them. The three-leaf strategy showed higher total dry mass (MST) of forage and leaf blade (MSLF) for maximum fertilization. The dead material mass (MSMM) decreased with increasing defoliation frequency. Thus, nitrogen fertilization favors growth and forage production, and in this study the maximum fertilization (180kg ha -1 N) provided greater yields in the two and three leaf emerged strategies.