Morphogenetic and structural characteristics of andropogon grass submitted to different cutting heights

Abstract

-This work was performed aiming to evaluate the morphogenetic and structural characteristics of Andropogon gayanus cv. Planaltina species submitted to three cutting heights (20, 27 and 34 cm). The three cutting heights were allocated in experimental units (12 m 2 ) in a complete randomized block design with three replications. The cuts were done when the light interception by the sward reached 95%. At this moment, the sward height revealed itself constant with values close to 50 cm. The lowest cutting height (20 cm) influenced negatively the final leaf blade length, the number of live leaves, the leaf lifespan, the stem elongation rate and the tiller population density, and it influenced positively the phyllochron and the leaf senescence rate. Probably, cuts at 20 cm height caused a high decapitation and death of the tillers. The worst growth conditions in addition to the blossom of this specie occurred during fall resulted in higher stem elongation rates and number of live leaves, and lower phyllochron, final leaf blade length, and leaf lifespan. The sward height can be used as a practical and efficient criterion in the management of andropogon grass. Under intermittent management conditions, the regrowth of andropogon grass must be interrupted when the sward reaches 50 cm height, and the defoliation must be interrupted when the stubble height is close to 27 cm.Key Words: Andropogon gayanus, ecophysiology, light interception, morphogenesis, sward height Características morfogênicas e estruturais do capim-andropógon submetido a diferentes alturas de corte RESUMO -Este trabalho foi realizado com o objetivo de avaliar as características morfogênicas e estruturais da espécieAndropogon gayanus cv. Planaltina, submetida a três alturas de corte (20, 27 e 34 cm). As três alturas de corte foram alocadas às unidades experimentais (12 m 2 ) em delineamento de blocos completos casualizados com três repetições. Os cortes foram realizados quando a interceptação luminosa pelo dossel atingiu 95%. A altura do dossel nesse momento mostrou-se constante, com valores próximos a 50 cm. A menor altura de corte (20 cm) influenciou negativamente o comprimento final da lâmina foliar, o número de folhas vivas, a duração de vida da folha, a taxa de alongamento de colmo e a densidade populacional de perfilhos, e positivamente o filocrono e a taxa de senescência de folhas. Provavelmente, cortes a 20 cm de altura causaram elevada decapitação e morte de perfilhos. As piores condições de crescimento junto do florescimento ocorrido durante o outono resultaram em maiores taxas de alongamento de colmos e número de folhas vivas e em menor filocrono, comprimento final da lâmina foliar e duração de vida da folha. A altura do dossel pode ser utilizada como critério prático e eficiente de manejo do capim-andropógon. Em condições de manejo intermitente, a rebrotação deve ser interrompida quando o dossel atingir 50 cm de altura, e a desfolhação, quando a altura de resíduo ficar próxima de 27 cm.

Tillering dynamics in pastures of guinea grass subjected to grazing severities under intermittent stocking

“…Given that the criterion for termination of regrowth was the same (95% of light interception), the density of basal tillers did not vary between the post-grazing heights or seasons with an average of 374, 356 and 386 of tillers/m 2 for the post-grazing heights of 30, 50 and 50-30 cm, respectively. Sousa et al (2010), evaluating the Andropogon grass and Sousa et al (2011), evaluating the Xaraes palisade grass subjected to different cutting heights, all performed when the canopy reached 95% of light interception, also reported no changes in density of basal tillers, corroborating, thus, the results obtained in this study.…”

Morphogenetic and structural characteristics of tillers of guinea grass of different age and grazing severities

“…However, the severity of defoliation still needs to be adjusted (Sousa et al, 2010;Sousa et al, 2011). When pasture conditions are maintained relatively constant throughout the year, severe grazing promotes a high potential of tissue renewal with high accumulation of leaf blades and effective control of stem accumulation, while lenient grazing results in increased stem accumulation, but in intense use of the pastures during favorable times for plant growth (Difante et al, 2009 a,b).…”

Morphogenesis in guinea grass pastures under rotational grazing strategies

“…In this experiment, the criterion for determining the beginning of grazing was the same in all treatments, i.e., 95% light interception, which does not characterize a condition of intense competition for light, may justify the absence of differences in leaf appearance rate, phyllochron, leaf lifespan, final leaf length, and leaf senescence rate in all post-grazing heights. Studies based on growth and development rates of the plants when 95% of light interception was used do not show differences between the intensities of defoliation tested for the Andropogon grass (Sousa et al, 2010) and Xaraes palisadegrass (Sousa et al, 2011). This shows that the post-grazing heights adopted were adequate for the guinea grass cv.…”

“…The use of morphogenesis to study growth and development of plants in sward allows for a better understanding of dynamics responses of the sward to defoliation (Silveira et al, 2010;Sousa et al, 2010Sousa et al, , 2011. In adequate environmental conditions (photoperiod, temperature, humidity and soil fertility), the plants accelerate their growth rhythm, increasing their leaf appearance and elongation rates (Marcelino et al, 2006) and their stem elongation rate (Mazzanti et al, 1994;Difante et al, 2008).…”