Light interception and distribution in horizontal and vertical canopies of red raspberries

Abstract

Light interception by several plantations of horizontally (New Zealand canopy) and vertically trained red raspberries was recorded at the start of flowering and at harvest. The maximum daily light interception was 81% of incident light, achieved by a vertical system in rows 2.5 m apart. Measurements of light distribution within the canopy showed improved light penetration with the horizontal compared to the vertical training. Calculated values of light interception from a computer model showed close agreement with measured values. Using published data on the effect of between-row spacing on yield, yield was found to be a function of light interception, calculated from the model. The model was then used to define the row spacing of the horizontal canopy system which would attain equivalent levels of light interception to those of the vertical system. Results of a small shading trial indicated that the cropping of the horizontal canopy was unlikely to suffer from the shade cast by the vegetative cane growing up in the row centre.