Non-structural carbohydrates in Marandu-grass pastures under different grazing intensities
Carbohydrates are the source of available energy for growth and plants survival. This concentration is reduced by occurrence of defoliation and subsequent regrowth. Thus, reduction being directly proportional to the intensity and frequency of defoliation. This study aimed to evaluate non-structural carbohydrate content on Marandu-grass pasture managed under three grazing management heights. The heights of 15, 25 and 35 cm were managed by beef steers grazing under continuous stocking. Evaluations of non-structural carbohydrates occurred from January to November, 2011, at the UNESP, Jaboticabal, SP. Data were analyzed by repeated measurements with grazing intensity, period and interaction as sources of variation in variance analysis using proc mixed from SAS. Root and shoot samples were collected monthly with a steel cylinder of 15 cm diameter and 13.7 cm high. The collected samples were washed and processed for further analysis. The non-structural carbohydrates content in shoots was not affected (P>0.05) by grazing heights, season and interaction grazing height and seasons of the year. In roots, the contents were affected by the seasons and the interaction heights and seasons of the year. Concentrations in roots were lower in summer compared to other seasons evaluated. There was linear fit (P<0.05) of grazing heights only in the autumn. Non-structural carbohydrates showed a linear response (P<0.05) and the highest average values observed for the levels of non-structural carbohydrates in the roots occurred in winter (158.61 g.kg-1), followed by those for autumn (114.13 g.kg-1), spring (101.00 g.kg-1), and finally the lowest place in the summer (47.30 g.kg-1). The decrease of values from winter to spring and summer was probably due to the improvement of weather conditions over the spring and summer months, which should have provided higher dry matter accumulation, which, in turn, demanded more organic reserves supply in order to have formed new tissue. Climatic changes conditions, defined by the seasons, provide changes in the levels of non-structural carbohydrates. Marandu-grass pastures grazed to 15 cm did not show a drastic condition management since it does not affect the reserve compounds from plants, when compared with the other hights studied.
Keywords: Reserve compound, roots, shoots.