Carbon assimilation and herbage accumulation of mulato II brachiariagrass under contrasting growth rates and sward heights maintained by continuous stocking

Abstract

Grazing management is key in ruminant production because it can directly affect primary aspects of forage production. Grazing intensity can modify canopy structure affecting their photosynthetic rates and promoting changes in the amount and distribution of light within the plant community. Grazing management is key in ruminant production because it can directly affect primary aspects of forage production. Grazing intensity can modify canopy structure affecting their photosynthetic rates and promoting changes in the amount and distribution of light within the plant community. Changes may occur due to shifts in leaf area index composition which is the sum of the areas of leaves at different ages and stages of development, and may have different rates of carbon assimilation. The aim of this study is to describe and explain the process of carbon assimilation by the sward under grazing as a result of the participation of leaves with different photosynthetic rates, as well as the herbage accumulation of hybrid brachiariagrass (Brachiaria spp.) Convert HD 364 (cv. Mulato II) in response to two contrasting growth rates and three canopy heights kept constant by continuous stocking and variable stocking rate. The study will be carried out at Escola Superior de Agricultura Luiz de Queiroz, USP, in Piracicaba-SP from December 2013 to April 2014 and December 2014 to April 2015 (two summer grazing seasons). The experimental design will be a randomized complete block in a 3 x 2 factorial arrangement, combining three sward heights (10, 25 and 40 cm) and two growth rates imposed by nitrogen rates (50 e 250 kg N ha-1 yr-1), with three replications, totalling 18 experimental units. Response variables studied will include leaf and canopy photosynthesis rates, canopy architecture, light extinction coefficient, herbage accumulation and plant-part composition of the herbage mass (proportion of leaves, stem + sheath and dead material). Data will be analyzed using Proc Mixed of SAS and the means will be compared by Student's T test with the level of significance set at 5%. (AU)