GROWTH HABIT AND ROW WIDTH EFFECTS ON LEAF AREA DEVELOPMENT AND LIGHT INTERCEPTION OF FIELD BEANS

Leaf area development and percent interception of photosynthetically-active radiation (PAR) were measured to compare a determinate, bush cultivar with an indeterminate, climbing or pole cultivar of Phaseolus vulgaris L. in a short season environment. Each cultivar was grown at a wide (91 cm) and narrow (45.5 cm) interrow spacing to evaluate the growth habit effects under currently recommended plant spacings. Percent PAR interception and leaf area index (LAI) were determined on five sampling dates and PAR penetrating through the canopy was recorded on four of those dates. A large reduction of LAI of the bush cultivar and continued expansion of leaves in the upper portion of the pole canopy resulted in a greater percentage of PAR interception by the pole cultivar than by the bush cultivar at 72 days after planting. The taller, unlodged vine-type canopy of the pole cultivar intercepted nearly 50% more PAR than the bush cultivar when the LAI of the two cultivars was comparable at 96 days. The continued leaf expansion and late initiation of pod filling limited the duration of rapid pod filling of the pole cultivar in the short season environment. LAI and percent interception of PAR by the bush cultivar were greater at the 45.5-cm than at the 91-cm spacing at 41 and 54 days. The maximum LAI and percent interception were only 3.2 and 82%, respectively, for the 91-cm spacing of the bush cultivar. LAI of the 45.5-cm spacing of the bush cultivar was reduced to a value less than that of the 91-cm spacing from 54 to 72 days, but percent interception by the 45.5-cm spacing was still greater. Percent interception of PAR at 41 days was greater at the 45.5-cm spacing than at the 91-cm spacing of the pole bean, but interrow spacing did not affect LAI or percent interception on the other dates.