A field experiment was conducted at the Bangabandhu Seikh Mujibur Rahman Agricultural University farm during early summer (Kharif I) season. The soil of the experimental plot was silty clay of red brown terrace under Salna series. The experimental site is characterized by hot-humid subtropical climate with abundant rainfall during monsoon season extending from May through September while the remaining part of the year evaporative demand exceeds rainfall. The mean atmospheric temperature ranges from 11.9°C (January) to 34.4°C (July). The experimental land was ploughed by a tractor and rotovator. A fertilizer dose of 20 kg N, 15 kg P and 20 kg K ha-1 as urea, TSP and MP, respectively, was applied basally at final land preparation and incorporated well into the soil. Six levels of planting densities each at three levels of configuration formed the treatment variables. Different configurations were created by varying the rectangularity keeping the density constant. The treatment combinations were arranged as follows: D1: 10 plants m-2 i.e. 1000 cm2 plant-1
D1C1: 31.50 x 31.50 cm (1:1), D1C2: 20.00 x 50.00 cm (1:2.5), D1C3: 15.00 x 66.50 cm (1: 5)
D2: 20 plants m-2 i.e. 500 cm2 plant-1
D2C1: 22.50 x 22.50 cm (1:1), D2C2: 14.00 x 35.50 cm (1:2.5), D2C3: 10.00 x 50.00 cm (1: 5)
D3: 30 plants m-2 i.e. 333 cm2 plant-1, D3C1: 18.25 x 18.25 cm (1:1), D3C2: 11.50 x 28.25 cm (1:2.5), D3C3: 8.00 x 41.52 cm (1: 5)
D4: 40 plants m-2 i.e. 250 cm2 plant-1
D4C1: 15.81 x 15.81 cm (1:1), D4C2: 10.00 x 25.00 cm (1:2.5), D4C3: 7.00 x 35.71 cm (1: 5),
D5: 50 plants m-2 i.e. 200 cm2 plant-1
D5C1: 14.14 x 14.14 cm (1:1), D5C2: 9.00 x 22.22 cm (1:2.5), D5C3: 6.25 x 32.00 cm (1: 5)
D6: 60 plants m-2 i.e. 167 cm2 plant-1
D6C1: 12.90 x 12.90 cm (1:1), D6C2: 8.00 x 20.87 cm (1:2.5), D6C3: 5.80 x 28.80 cm (1: 5)
The experiment was laid out in a Factorial Randomized Complete Block Design with three replications. Unit plot size was 4x3 m. Seeds were sown in rows as per treatment. Seeds were pre-soaked for 3 h before sowing. Light irrigation was applied one day after sowing. The variety used in this study was NM 92, an advanced line obtained from the Asian Vegetable Research and Development Center (AVRDC), Taiwan. Seedlings emerged by 4 days after sowing and gap filling was done using even aged seedlings on the following day of emergence (DAE).
At first trifoliate stage seedlings were carefully thinned to retain one seedling per hill. Soil mulching and hand weeding were done twice at 13 and 21 days after sowing (DAS). Irrigation was applied twice at 15 and 25 DAS. Insecticide (Ripcord) was sprayed on four occasions to keep the insect infestation to a minimum. Urea at the rate of 20 kg N ha-1 was side dressed at 20 DAS. Plant samples were taken at weekly interval beginning at 12 DAE. Three plants from each of the lower density treatments 10, 20 and 30 plants m-2 and 5 plants from each of high density treatments 40, 50, 60 plants m-2 were sampled. Plants were cut at the base, put in polythene bag to prevent desiccation of leaves and were brought to the laboratory. Plant parts were separated into stem, petiole, leaf and reproductive organs and oven dried at 70°C for 72 h. Weights of individual components were recorded. Standard regressions were used to describe allometric relationships. The fact that plant form variables co-vary was, however, ignored. The parameters considered to be least influenced by plant characters were used as independent variables. In all cases variables were log transformed before regressions were obtained.