Potential Photosynthesis in Trellis-Type Orchard Canopies.

Abstract

The choice of fork angle in orchards of the Tatura trellis design is investigated through simulations of the light relations and resultant photosynthetic response of a variety of structural alternatives. Computations consider a treatment of the penetration of direct solar beam on which is superimposed either a simplified or a complex treatment of the diffuse radiation climate within the orchard canopy. Computations show that, at any leaf area index, the potential seasonal photosynthesis of a flat canopy (fork angle = 180°) sets the upper limit to the productivity of all canopies of lesser fork angle. The diffuse component of radiation has a significant influence on expected absolute harvest yields, reducing the relative differences in yields between canopies of various fork angles which result from the strong interaction between solar trace and canopy geometry. The commonly selected fork angle of 60° cannot be defended on the basis of maximum seasonal potential photosynthetic productivity.