Effect of planting density by cultivars on the growth and yield of melons (Cucumis melo l.) in hydroponics using coir substrates

Abstract

This study aimed to evaluate the effect of planting density by cultivar on the growth, quality, and yield of melon (Cucumis melo L.) in hydroponics using coir substrates. Experiments were conducted using three domestic netted melon cultivars, namely ‘Earl’s Kingstar’, ‘Hero’, and ‘PMR Dalgona’. The plants were transplanted on March 19, 2019 to a venlo-type glass greenhouse. The spacing between the rows was 1.5 m and the planting density was 2.0, 2.7, and 3.3 plants/m2 (the within-row planting distance was 0.33, 0.25, and 0.20 m, respectively); the plants were grown using slabs of equal sizes (100 × 20 × 10 cm). The electrical conductivity (EC) levels in the supplied nutrient solution were 1.8 and 2.1 dS∙m-1 after transplanting and fruit setting, respectively. The EC level in the drained solution was less than 1.0 dS∙m-1 in the early stages of growth; it increased to 3.0 dS∙m-1 in the middle stages with the increase in irrigation, and in the late stages of growth, it was about 4.0 dS∙m-1 in all the treatments. The planting density did not have any significant effect on the EC level and pH of the drained solution. An evaluation of the growth of all the three cultivars showed that the lower the planting density, the larger the stem diameter, leaf length, leaf width, and leaf area of the plants. The lengths from 0 to 10th node tended to be small when the planting density was 2.0 plants/m2, and the node length from 10th to 20th node did not differ among different plant densities. The lower the planting density, the heavier the fruit in all the three cultivars and the higher the soluble solids content. However, the yield increased by 20.8 to 32.6% as the planting density increased from 2.0 to 3.3 plants/m2. For ‘PMR Dalgona’, the rate of decline in average fruit weight was the lowest by 19.6% and the rate of yield increase was the highest by 32.6% when increasing the planting density from 2.0 to 3.3 plants/m2. For ‘Earl’s Kingstar', on the other hand, the rate of average fruit weight decreased the most by 26.8% and the rate of yield increased the least 20.8%. The heavier fruit weight had a large decrease in the average fruit weight by planting density, which showed the sensitivity of planting density depending on cultivars. Therefore, this study suggests that cultivars with a higher planting density with greater production per unit area have an advantage from an economic point of view, whereas the lower planting density is reasonable in terms of fruit quality.