Objetivou-se avaliar o estado nutricional do capim-xaraés utilizando o clorofilômetro SPAD e estabelecer o índice de suficiência crítico (ISNc) nas épocas das águas e seca. O experimento foi conduzido em um delineamento inteiramente casualizado com quatro tratamentos (50, 100, 200 e 400 kg N ha-1), três repetições, duas épocas: águas e seca. Todas as variáveis apresentaram alta relação não linear com seus preditores (p < 0,001). O nitrogênio total (NT) alcançou o platô na dose de 262,0 e 514,8 kg de N ha-1 e a concentração de NT na planta foi 1,88 e 1,93% no período das águas e seco, respectivamente. O teor relativo de clorofila (TRC) atingiu o platô a 46,05 e 53,65 unidades SPAD no período das águas e seca, respectivamente. A produção de matéria seca (MS) apresentou máxima resposta a adubação nitrogenada na dose de 209,5 e 229,1 kg N ha-1 na época das águas e seca, respectivamente. O índice de suficiência de nitrogênio (ISN) atingiu o platô em 0,85 e 0,99 na época das águas e secas respectivamente. Todas as variáveis apresentaram alta correlação linear (r= 0,71 a 0,99). O ISNc do capim-xaraés é 0,85 e o clorofilômetro pode ser utilizado como ferramenta de manejo nutricional de N para essa gramínea.

The nutritional status of xaraes palisade grass with SPAD chlorophyll meter and the critical nitrogen sufficiency index (cNSI) in the dry and rainy seasons were assessed. The experiment was conducted in a completely randomized design with four treatments (50, 100, 200 and 400 kg N ha-1), three replicates and two seasons: dry and rainy. All variables had a high nonlinear relationship with their predictors (p < 0.001). Total nitrogen (TN) reached a plateau at doses 262.0 and 514.8 kg of N ha-1 and the concentration of TN in the plant was 1.88 and 1.93% respectively during the rainy and dry season. Relative chlorophyll content (RCC) reached a plateau at 46.05 and 53.65 SPAD units in the rainy and dry seasons, respectively. The production of dry matter (DM) showed maximum response to nitrogen fertilization at 209.5 and 229.1 kg N ha-1 during the rainy and dry season respectively. The nitrogen sufficiency index (NSI) reached the plateau at 0.85 and 0.99 in the rainy and dry season respectively. All variables showed high linear correlation (r = 0.71 to 0.99). The xaraés palisade grass's cNSI is 0.85 and the chlorophyll meter may be used as a nutritional N management tool for the grass.

The experiment was carried out on Cynodon spp cv. Tifton 85 pastures grazed by sheep under rotational stocking, with the objective of evaluating the structural characteristics as well as the forage mass of the pastures subjected to three grazing intensities in successive cycles. Treatments were composed of three residual leaf area indices (rLAI; 2.4; 1.6 and 0.8), allocated in completely randomized blocks with seven replications, totaling 21 experimental units. Tiller population density, pasture height, leaf area index, forage morphological composition and pasture forage mass were evaluated. The rLAI modified the tiller population density, which increased linearly with decrease in the rLAI of the pastures. Dry masses of leaf blade, stem and dead material were inferior when the rLAI imposed were lower, which resulted in differentiated forage production among the treatments. Tifton 85 pastures grazed by sheep in rotational stocking under tropical conditions with different rLAI show a modified sward structure over successive grazing cycles, mainly by alteration in the height and LAI of the plants at pre-grazing and by light interception post-grazing, which change the tiller population density. The residual leaf area index of 1.6 is the most suitable for pasture management for being equivalent to the heights of entrance and exit of animals on and from paddocks of 33 and 19 cm, respectively, which avoid great accumulation of dead material and excessive stem elongation, in addition to ensuring tillering in the sward.

This study was carried out to analyze the tillering profile of Guinea grass (Panicum maximum cv. Tanzania) pastures subjected to two grazing frequencies (time necessary to intercept 90 and 95% of the incoming light) and two post-grazing heights (30 and 50 cm) in the period from November 2005 to October 2006. The experimental design was of completely randomized blocks with three replications, in a 2 × 2 factorial arrangement. At the end of the spring, pastures managed with 90% light interception showed greater tiller appearance rates in relation to pastures managed with 95%, regardless of post-grazing height. In the summer and fall, pastures managed with post-grazing height of 30 cm showed higher tiller appearance rates in comparison with pastures managed at 50 cm, regardless of grazing frequency. Concerning the tiller mortality rates, in the summer, higher values were found for pastures managed at 90/50 and 95/30 (interception/height), intermediate values at 90/30 and lower values in those managed at 95/50. Pastures managed at 90/30, 95/30 and 95/50 in the fall presented greater tiller mortality rates than those managed at 90/50. These differences do not occur in the winter/beginning of spring. The stability index remained above 1 all through the experimental period. All management strategies evaluated are adequate for Guinea grass.