Phyllochron and Leaf Lifespan of Four C4 Forage Grasses Cultivated in a Silvopastoral System

Silvopastoral systems are emerging as an option for more sustainable land use. However, the challenge is to optimize pasture production and the determine suitable management by understanding the growth and development of forages under trees canopy (Palma et al. 2007). In the silvopastoral system, trees change the environment that forages grow, and can influence the development of plants and, consequently, the sward dynamics. For instance, the light quantity (i.e. photon flux density) and quality (e.g. changes in red: far-red ratios) can vary as a result of the tree canopy (Beaudet et al. 2011). Phyllochron and leaf lifespan are morphogenetic processes that control growth and development of plants in a specific environment. These processes determine leaf area index and so the light interception by the sward (Lemaire and Chapman, 1996). These two characteristics can be used as tools for pasture management, and also are influenced by management practices, like nitrogen fertilization. However, there are few studies that evaluated these characteristics for forages cultivated under tree canopy (Paciullo et al. 2008), particularly when using the light interception (LI) as a criteria for cutting frequency. Under full sun, rotational stocking using 95% canopy LI has been recommended to use C4 species to their fullest potential and optimize ruminant weight gains on pasture (Silva and Carvalho, 2003). The aim of our work was to determine both the shading (five-year-old plantation of Eucalyptus dunni) and nitrogen availability effect on phyllochron and leaf lifespan of four C4 forage grasses species in a sub-tropical region, managed using the 95% light interception criteria to determine cutting frequency