Responses of Vegetable Soybean to Irrigation Frequency and Plant Density

Abstract

Water availability and plant density are major factors related to crop growth and yield. The experiment was conducted to examine the response of the vegetable soybean variety, Chiang Mai 1, to irrigation frequency and planting density on the sandy laam soil at Phitsanulok Field Crops Experiment Station in 1999/2000 growing season. A split plot design with 3 replication was used. Three irrigation frequencies, irrigation applied after every 30 (E30), 60 (E60) and 120 (E120) mm/ were deployed as main plots. Sub-plots were plant densities of 332,000 , 64,000 and 96,000 plants/rai. There were no interactions between irrigation frequency and plant density in growth , yield and yield components. E30 and E60 showed no significant differences in leaf area index (LAI), crop growth rate (CGR) and leaf area duration (LAD), whereas, E120 gave smaller LAI, CGR and LAD, LAI, CGR and LAD significantly increased with increasing plant densities from 32,000 to 64,000 plants/rai.
E30 produced yield (pods + stem) and pod fresh weight similarly to E60 but had 34% greater yield and pod fresh weight than E120. Increases by yield and pod fresh weight of high irrigation frequencies resulted from increasing seed fresh weight and pods/plant. A significant yield (15 and 28%) and pod fresh weight (14 and 28%) reduction was asociated with reducing plant densities from 96,000 to 65,000 and 32,000 plants/rai, respectively. The number of plant harvested was a major factor determining a greater yield and pod fresh weight of high densities, although seed fresh weight and pods/plant reduced with increasing plant densities.