Investigation on Application Amount of Potassium in Limited Nutrient Supply Control of Tomatoes Grown in Substrate Culture Using Double Trough Bed

To investigate the suitable amount of potassium supplied to tomato plants through a limited nutrient supply control on substrate culture, tomatoes were grown until the 6th truss pinching stage in a substrate culture using a double trough bed with granulated rockwool. In the EC-based control method (control), nutrient solution was applied using a free drainage system. In the limited nutrient supply method, 250 mL of nutrient solution containing 3 levels of potassium (15, 30, 50 me K·plant−1·week−1) was supplied to each plant. Results showed that there was no significant difference in the yield of the 1st to 3rd trusses. In the 4th to 6th cluster, the yield was lower in plants receiving 15 me K·plant−1·week−1 treatment compared with that of controls, but there was no significant difference in plants receiving 30 and 50 me K·plant−1·week−1. However, in plants receiving 30 me K·plant−1·week−1 treatment, vascular browning was observed from the 2nd cluster to the 6th cluster with an incidence of 16 percent in the latter. The ratio of the total amount of potassium applied during the experiment at 15, 30 and 50 me K·plant−1·week−1 treatment to that of control was 28, 56, 98%, respectively. Based on these findings, in the 6th truss of tomato grown on substrate culture considerable reduction of potassium supply caused a physiological disorder in the tomato fruit. Therefore, in the EC-based control method supply, it was necessary to increase the potassium supply from 30 me K·plant−1·week−1 to 50 me K·plant−1·week−1 during the early stage of the 2nd truss of fruit development.