Reducing sodium accumulation in the root environment of tomato in a closed-loop cultivation system using a split root system

In closed-loop greenhouse crops, sodium (Na) accumulation in the recirculating solution will result in a discharge of water and nutrients if the Na input is higher than the plant uptake. Based on the findings that plants will tolerate high electrical conductivity (EC) when grown with a split-root system with one root half exposed to high EC and the other half is irrigated with a normal EC. It was suggested that this would apply to Na as well. The objective was to study if plants can tolerate higher Na and take up more Na by using a split root system and secondly if a small part of the nursery equipped with a split root system can alleviate Na accumulation for the whole nursery. A first trial confirmed split root tomatoes prefer to absorb water from the low EC side, while Na uptake increased with the rising Na concentration. A second greenhouse trial with split root gutters in a section of a standard rockwool tomato cultivation, had an increased Na input through the water source. This trial ran for 6 months with a fully closed recirculation system. The drainage solution from the standard gutters was discharged into the Na-treated root halves of the split-root setup. Three Na target concentrations (12, 25, 30 mmol L-1) were tested (EC consequently: 3.5, 6, 8 dS m-1) in the Na-treated halves. The results showed it is possible to increase the overall Na uptake of the closed system without loss of production in the standard rows. The yield of the split root rows exposed to high Na was 10% reduced, but the fruit quality increased.