Tomato plants were grown in closed cultivation systems, either in rockwool or in flowing nutrient solution.
The rockwool system was arranged in a traditional way with drip irrigation.
In the other systems rockwool cubes (0.6 dm3) were submerged to half their depth in a continuously flowing nutrient solution (NFT) in which the root system grows.
The cultivars used were ‘Elin’ and ‘Gitana’.
In the rockwool system and in one of the systems with NFT the N/K ratio was 100/47 based on mM. The potassium content was increased in the other system with NFT, giving a N/K ratio of 100/54 based on mM. The total yields were about the same in all three systems.
However, the fruit quality was poorer in the system with NFT and weakest potassium concentration.
Every third week, plants were harvested from the rockwool system.
The dry weights and contents of nutrients were determined for different plant parts during the growth season.
The season was divided into three periods: February-March, April-August and September-November.
The relative sink strengths between fruits and vegetative plant parts were calculated for these periods.
Even the mineral nutrient concentrations in the dry matter of fruits and vegetative parts were calculated.
The results were used to determine the nutrient compositions that have to be supplied to the system in different periods of the growth season, in order to maintain the nutrient composition in the root environment at the desided level.
The amount of the total nutrient supply varies according to the growth rate, and is regulated by continuously adjusting the EC value.