Development of fertigation system for tomato bag culture based on cumulative solar radiation and vapor pressure deficit values

In order to develop the feasible fertigation system, tomatoes "Momotaro Fight" were grown in bag culture system with drip irrigation equipments using coconut coir as substrate. The growth stage was separated into 5 stages for supply different amounts of nutrients and water. In this system the setting amount of nutrient was supplied when the cumulative solar radiation (CSR) value reached 1 MJ m². The setting amounts increased gradually (from 0.23-0.40 me plant ¹ MJ^-1 m²) with the process of growth stage. There were 4 treatments with varying levels of water supply for vapor pressure deficit (VPD) as follows: V-0 (no additional supply of water), V-20, V and V-20. In the V-0 treatment, the highest contents of total soluble solids in the fruits were recorded, while the values of the leaf dry weight, photosynthetic rate and yield were the lowest. The V and V+20 treatments were associated with a lower percentage of drainage (5-7%), higher water use efficiency and nitrate use efficiency while salt accumulation inside the substrate could be avoided. With these 2 treatments a highly efficient fertigation system based on CSR and VPD values was developed for the production of low truss tomato production system.