PLANT SPACING EFFECTS ON LIGHT INTERCEPTION BY GREENHOUSE TOMATOES

Abstract

The effect of six equidistant spacings (23, 30, 38, 45, 53, 60 cm) on interception of photosynthetically active radiation (PAR) by four-row plantings of greenhouse tomato (Lycopersicon esculentum Mill. ’Jumbo’ and ’CR-6’) was studied. A silicon cell sensor was used to measure PAR in and around the test plant canopies. These observations were used to construct canopy profiles of PAR absorption, as affected by plant spacing and cultivar. Measurements under both clear and overcast skies revealed no major differences in the pattern of PAR interception within a canopy due to the presence or absence of direct light over the sampling period. The proportion of available PAR intercepted increased with closer plant spacing, but PAR penetration increased and distribution improved with increasing plant spacing. An increasing degree of self-shading of the central and north parts of the canopies was evident with closer planting. Plant spacing also had a large effect on the quality of canopy transmitted light. The ratios of blue:far-red, red:far-red and blue:red light transmitted through the four-row canopies of both cultivars decreased with decreases in plant spacing and in general were lower under the canopies of CR-6, than under the canopies of Jumbo.Key words: Tomato, Lycopersicon esculentum Mill., plant spacing, light interception