Influência da adubação nitrogenada nos parâmetros luminosos, morfogênicos e produtivos em diferentes materiais genéticos de Urochloa

Abstract

The objective of carrying out this work was to evaluate the influence of nitrogen fertilization in different Urochloa genotypes on light, morphogenic and productive parameters in field conditions. The project was carried out in the experimental area of Forage and Pastures/Agrostological Field – UFGD, where 8 cultivars were planted, namely: Marandú, Ruziziensis, Ipyporã, 780 J, Mulato II, Sabiá, Cayana and Mavuno, with 2 doses of nitrogen fertilizer ( 100 and 200 kg of N/ha) and 4 replications per treatment, totaling 64 beds, implemented in 2020. The productivity variables analyzed were: Forage Canopy Height (FCH, Total Dry Mass Productivity (TDMP), Proportion of Leaves and Stems (PL and PS), Leaf:Stem Ratio (LSR) and Dry Matter Content (DMC). The morphogenic parameters were analyzed by monitoring 6 tillers per bed, namely: Number of Live Leaves (NLL), Leaf Length (LL), Leaf Width (LW), Phyllochron, Appearance Rate (LAR), Elongation (LER) and Leaf Senescence (LS) and Stem Elongation Rate (SER). As for the Light Parameters, Light Interception (LI) and Leaf Area Index (LAI) were evaluated at different times of forage growth. All data obtained were subjected to the Scott-Knott Test at a level of 5%. A positive interaction was observed between cultivars and nitrogen doses for FCH, PL, PS, LSR, LW, Phyllochron, LAR, LER, SER and LAI. A greater productivity (t of leaves/ha/year) of leaves was noted for the cultivars Cayana (14.22), Sabiá (13.83) and Mulato II (17.12), corresponding to 88.31, 85, 06 and 89.68%, respectively, of total production. There was also a marked response in canopy height and productivity in the cultivars Ipyporã, 780J and Ruziziensis, due to fertilization, even at lower doses. There is a disparity in the cultivars' responses, which raises the assumption that the use of general management recommendations may not exploit the forage potential of these new materials, thus ending the need to adopt specific and precise management for each material. . It was concluded that the cultivars behaved differently in terms of productivity and leaf and stem production, in addition, it was noticed that the standardization of the cutting height at 30 cm, regardless of the cultivar and time of year, does not reflect 95% of IL, therefore, the adoption of management with fixed height could underestimate the forage potential, especially of hybrid materials. Furthermore, the use of light parameters as a tool for pasture management, as they are influenced both by the morphogenic responses of forages throughout the year and by nitrogen fertilization, providing specific and flexible information depending on the technologies used in a pasture area, thus being able to infer the idea of precision pasture management.