Produção e composição bromatológica do capim marandu adubado com nitrogênio e potássio

Abstract

The objective was to evaluate the influence of nitrogen and potassium doses on the production and bromatological composition Urochloa brizantha cv. Marandu. The experiment was carried out at the Experimental Farm of the Federal University of Mato Grosso, Cuiabá campus, from December 2017 to September 2018 and from December 2018 to September 2019. The experiment was installed in a completely randomized design with 4 replications. The treatments were arranged in a 5x2 factorial scheme, with five doses of nitrogen (0; 25; 50; 75; 100 kg ha-¹) and two doses of potassium (0; 25 kg ha-1) at each defoliation cycle. The bromatological characteristics evaluated were: crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), indigestible neutral detergent fiber (iNDF), total digestible nutrients (NDT) and lactation net energy (ELL). The productive characteristics were: accumulation of total dry mass (AMST), forage participation (PARTFOR) (%) and soil cover (COBSOL) (%), percentage of leaf blade dry mass (MSFL) (%), percentage of mass stem dryness + sheath (MSCB) (%), number of total tillers (NPT). For bromatological composition variables, a positive linear effect was observed in CP for nitrogen fertilization, being 15.87% and 11.68% for the highest dose applied in the wet and dry seasons, respectively. Likewise, a linear increase in NDT and ELL content was observed. For NDF, ADF and NDFi there was a reduction in the order of 0.11%; 0.07%; 0.05%; and 0.05%; 0.04%; 0.02% for each kg of N applied in the wet and dry seasons respectively. For the bromatological composition, potassium has an effect only in the rainy season for the fiber, NDT and ELL contents. Thus, nitrogen fertilization provides an increase of 51.13% in CP content at the highest applied dose. NDF levels; FDA; NDFi linearly reduce the application of nitrogen, on the contrary, there is an increase in NDT and ELL. For production variables, AMST had its maximum production point at a dose of 78.6 kg N ha-1, with production of 12,575 kg MST ha-1 in the presence of potassium, potassium increased by 79.8 kg/AMST for each kg of K applied to water. For %MSFL in the rainy and dry season, an increase in production of 10% and 36%, respectively, was observed in the presence of potassium. For NPT in the rainy season, there was an increase of 3.9 tillers for each kg of nitrogen applied, obtaining a maximum production of 946 tillers per m².