Abstract
Photosynthetically active radiation (PAR) was measured under three upland rice cultivars of contrasting canopy depth grown at wide spacing. The fraction of PAR transmitted to a point at or near the soil surface was related to canopy depth, leaf area index (LAI) and the ratio of sensor height to canopy depth. The minimum combination of plant height and LAI necessary to reduce PAR at soil level by 85 and 95 per cent, and so inhibit weed growth, was calculated.
