Prediction of Soluble Solids of Tomato Fruit Grown in Salinized Nutrient Solution Based on the Electrical Conductivity of the Drainage

Summary

This field study in Japanese commercial tomato greenhouses developed a predictive model linking cumulative electrical conductivity of drainage solution (from flowering to harvest) to final fruit Brix content. The linear regression model was validated across multiple experiments with different cultivars, substrates, and irrigation systems, demonstrating that growers can target specific EC levels during production to achieve desired soluble solids (≥6% Brix) with >86.9% fruit quality compliance and >88.2% marketable yield. The model offers a practical, non-destructive method for real-time monitoring and control of tomato sweetness in commercial greenhouse operations.

Regional applicability

The study was conducted in Japanese greenhouse systems and may have direct application to similar controlled-environment horticulture in the United Kingdom, particularly indoor and protected tomato production. Transferability to UK field-grown tomatoes would depend on climate, soil type, and water management differences; however, the EC-based monitoring approach is applicable to any substrate-based or soilless system used in UK commercial horticulture.

Key measures

Fruit Brix (soluble solids %), electrical conductivity (EC) of nutrient solution and drainage, cumulative EC of drainage (cECd), root mean square error (RMSE) between observed and predicted Brix, marketable yield percentage

Outcomes reported

The study developed and validated a linear regression model to predict tomato fruit Brix (soluble solids content) based on cumulative electrical conductivity of drainage solution from anthesis to harvest. The model was tested across multiple growing seasons, cultivars, and substrate systems to enable growers to manipulate nutrient EC to achieve target fruit quality.

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