Defoliation patterns and tillering dynamics in Italian ryegrass under different herbage allowances
This work was carried out in order to generate information on the tillering process and to contribute for the understanding of the defoliation process on Italian ryegrass (Lolium multiflorum Lam.) grazed by lambs under different herbage allowances: 6, 8 and 12 kg of dry matter per 100 kg of animal live weight per day. The grazing method was intermittent. The experimental design was completely randomized following a repeated measure arrangement, with three treatments and two area replications. The intensity of defoliation is greater at 6 and 9% herbage allowances. The defoliation interval is higher at 12% herbage allowance, intermediate at 9% and lower at 6%. The rates of tiller emergence, survival and death, stability index the tiller population are similar for the different herbage allowances and differ according to the phenological stage of ryegrass. Structural changes caused by canopy management with low herbage allowance and/or due to the advance in developmental stage of ryegrass alter defoliation strategies, with more intense and frequent grazing.
Energy flows and organic reserves of forage plants
This review addressed the existing energy flows in the pasture ecosystem, as well as the use of organic reserves by forage grasses. The radiant energy is absorbed by the leaves and transformed into chemical energy by which the assimilated carbon is fixed. During the process of assimilation and fixation of C, photochemical, and biochemical processes are carried out, which are influenced by light. Several environmental factors can influence the ability of plants to respond to stimuli. In this sense, energy flows within the pasture system are in constant movement to maintain the forage plant. The direction of energy flow varies with the growth environment of the forage plant, since in addition to affecting the structural characteristics, the environmental factors exert control over the root system. In theory, organic reserves located in roots and stems play a crucial role in the growth of grazed plants, especially in the first days after defoliation. Therefore, it is important to encourage research involving the reserve organs and their accumulation patterns so that the results can assist in the development of sustainable grazing systems.
Dinâmica do acúmulo de matéria seca em pastagens de Tifton 85 sob pastejo
Herbage dry matter accumulation from forage plants results from the balance between growth and senescence. Agronomic practices may influence both processes in different ways and, therefore, alter the quantitative and qualitative patterns of dry matter production. This study aimed at evaluating the process of dry matter accumulation through measurements of growth and senescence. Experimental treatments corresponded to four sward state conditions (5, 10, 15 and 20 cm of sward surface height - SSH) generated by sheep grazing under continuous stocking and variable stocking rate. The experimental design was a complete randomised block, with four treatments and four replicates. Pasture responses evaluated were: stem elongation, leaf lamina elongation, senescence, phyllochron and number of leaves per tiller. The results showed a seasonal pattern of herbage production with the highest growth and senescence rates observed at the highest SSH studied (15 and 20 cm). Phyllochron varied according to time of the year and SSH, revealing an intimate relationship with air temperature variation, soil water availability and sward leaf area index. SSH of 15 and 20 cm resulted in the highest dry matter production. The same principles and relationships originally described for herbage accumulation in temperate grass pasture species are valid for tropical areas within the framework of the physiological and environmental constraints inherent to each condition.