Análise de crescimento do capim-marandu submetido a doses de nitrogênio Growth analysis of marandugrass in response to nitrogen rates

Marandu, submetida a doses de nitrogênio (N) na solução nutritiva (28, 112, 210, 294 e 378 mg/L, na proporção constante de 70%:30% entre N-NO3- e N-NH4+), em diferentes idades de crescimento (21, 28, 35, 42, 49 e 56 dias após a emergência). O experimento foi conduzido em casa-de-vegetação, em solução nutritiva, e utilizando sílica como substrato. O delineamento experimental foi o de blocos completos ao acaso, com quatro repetições, em arranjo fatorial 5x6. As doses de N e as idades de crescimento interagiram significativamente em todos os atributos de crescimento do capim-marandu, com exceção da taxa de assimilação líquida (TAL). Constatou-se valor máximo para a taxa de crescimento relativo (TCR) e taxa de crescimento absoluto (TCA), respectivamente, de 0,25 g/g.dia à idade de 28 dias, com o N na solução em 378 mg/L e 3,68 g/dia, aos 56 dias de crescimento, com a dose de N de 378 mg/L. Aos 21 dias de crescimento, verificaram-se valores máximos de 2,16 dm²/g para a razão de área foliar (RAF), com a mais alta dose de N, 0,48 g/g para a razão de massa foliar (RMF), com N na dose de 294 mg/L e de 5,14 dm²/g para a área foliar específica (AFE), com o suprimento de N na solução em 378 mg/L.<br>This research was conducted with the objective of determining growth of Brachiaria brizantha (A. Rich.) Stapf. cv. Marandu under nitrogen (N) rates (28, 112, 210, 294 and 378 mg/L, where N-NO3- : N-NH4+ of 70%:30% proportion was kept constant) and growth ages (21, 28, 35, 42, 49 and 56 days after seedling emergence). The experiment was carried out in greenhouse conditions, with nutrient solution and using ground quartz as substrate. The experimental design used was a complete randomized block design, with treatments arranged in a 5x6 factorial, with four replications. Nitrogen rates and growth ages interaction was significant for all growth attributes of Marandugrass, except for the mean net assimilation rate (NAR). The results showed that the maximum values for the relative growth rate (RGR) and absolute growth rate (AGR) were 0.25 g/g.day and that was observed at 28 days with N rate at 378 mg/L, and 3.68 g/day at 56 days associated to N rate at 378 mg/L, respectively. At 21 days of growth, occurred maximum values of 2.16 dm²/g at the highest N rate for leaf area ratio (LAR), of 0.48 g/g with N rate at 294 mg/L for leaf weight ratio (LWR), and of 5.14 dm²/g for specific leaf area (SLA) at N rate of 378 mg/L.