MIXTURE OPTIMISATION OF THE MINERAL NUTRITION OF TOMATOES IN RELATION TO MINERAL CONTENT OF THE FRUIT: EFFECTS OF PREHARVEST FACTORS ON FRUIT QUALITY

Using “design and analysis of mixture systems”, a {3.1} simplex lattice design extended with the overall centroid was set up in the cation factor space (potassium, calcium and magnesium) and was repeated for two moisture contents (40 and 80 volume %).

Since a good knowledge of the chemical reactions occurring in nutrient solutions is the first prerequisite in hydroponic plant nutritional research, the elemental composition of the nutrient solutions after use was investigated.

Higher moisture content of the substrate yielded a higher production, due to the production of more tomatoes of the same weight.

Increasing the potassium, calcium and magnesium concentration of the nutrient solution resulted respectively in a higher potassium, calcium and magnesium content of the fruit. No interaction effect on fruit mineral content was found between moisture content of the substrate and mineral content of the nutrient solution.

Due to the importance of the moisture content of the substrate on fruit properties, an additional experiment with lower moisture content (30 – 50 volume %) was carried out.

This study demonstrates the usefulness of mixture theory for investigating the effect of preharvest mineral nutritional factors on fruit quality.

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