Photosynthetically active radiation use efficiency of Dactylis glomerata and Schedonorus phoenix along a hardwood tree-induced light gradient

Photosynthetically active radiation use efficiency (PARUE) of orchardgrass (Dactylis glomerata L.) and tall fescue (Schedonorus phoenix (Scop.) Holub) was determined. Leaf mass was harvested for canopies at different shade levels when each reached 20 cm height with 5 cm residue for regrowth to simulate grazing. Total incident PAR at each site was summed for the growth period (S-PAR). Values for PARUE were calculated from dried leaf mass divided by S-PAR. The more highly shaded plants reached 20 cm at lower S-PAR. While overall leaf mass decreased linearly with shade induced decreases in S-PAR, PARUE increased exponentially. The coefficients for the equations representing this exponential increase vary for forage species and may represent a useful index for characterizing forage response to silvopastoral systems.