Diomides S. Zamora

Interspecific Competition in a Pecan-cotton Alley-cropping System in the Southern United States: Is Light the Limiting Factor?

The manner in which light is intercepted by crop canopies and converted to structural dry matter can significantly affect primary production at a given site. A number of authors have investigated plant performance under different environmental conditions, including different levels of light, in alley cropping and similar agroforestry systems (Azam-ali et al. 1990; Monteith et al. 1991; Rosenthal and Gerik, 1991; Heitholt et al. 1992; Chirko et al. 1996; Gillespie et al. 2000; Jose et al. 2000). These studies have revealed strong linear relationships between photosynthetically active radiation (PAR, 400–700 nm) and dry matter production. Plants that develop under low levels of PAR such as in agroforestry systems grow and develop differently than plants grown under full sun (Monteith et al. 1991; Lambers et al. 1998). The amount of intercepted PAR becomes the major determinant of biomass production when belowground resources are not limiting. This relationship has been conceptualized as the time integrated product of three factors (Monteith et al. 1991):