SENSOR FOR ION-CONTROL – AN APPROACH TO CONTROL OF NUTRIENT SOLUTION IN HYDROPONICS –

Recently, hydroponics such as NFT and rock wool culture have been remarkably progressed in protected cultivation and plant factory.
In hydroponics, in order to have a good harvest of high quality, the control of the root zone, especially, of the ion concentration of the nutrient solution, is the most important.
Furthermore, physiological disorders by ion deficiency such as blossom-end rot of fruit in tomato cultivation will also be solved by means of the optimum control of the ion concentration.

While the conventional control of the nutrient solution have been performed based on only the level of EC and pH, ion sensors have been developed and examples of measurements have been reported.
In this paper, in order to have a detailed understanding of the ion uptake by plant for constructing data-base on the control of the nutrient solution, the dynamics of the ion concentration and the ion uptake by the plant of three sorts of ions (Ca²⁺, K⁺ and NO₃^–) were investigated, using an ion sensor developed for hydroponics.
The experiment was carried out in NFT (nutrient film technique) in the summer of 1988, cultivating tomato.
The ion sensor used in the experiment was Toshiba Model LQ201, which has three ion selective electrodes for Ca²⁺, K⁺ and NO₃^– in itself.

The concentration of Ca²⁺ in the nutrient solution was high during all the growth period, caused by low uptake of Ca²⁺ by plant.
On the other hand, as the K⁺ uptake was high, the deficiency of K⁺ in the nutrient solution was observed.
This tendency was remarkable in the developmental stage of fruit.
As for NO₃^–, there was a slight deficiency before the beginning of renewal of the nutrient solution, but after that NO₃^– in the nutrient solution was sufficient.
These results indicate that Ca²⁺ and K⁺ are reasonable ions to be monitored for control of nutrient solution in hydroponic tomato cultivation.

Introduction of ion sensor in hydroponics will make it possible to monitor the ion concentration, to make diagnosis of the plant and the nutrient solution based on data-base, and to make a reasonable control of the nutrient solution, resulting in having a good harvest of high quality.

I International Workshop on Sensors in Horticulture

T. Morimoto, H. Nishina, Y. Hashimoto, H. Watake

multi-ion sensor, nutrient concentration, NFT tomato

https://doi.org/10.17660/ActaHortic.1992.304.34