CATION CONCENTRATIONS OF PLANT TISSUES OF FRUIT-VEGETABLE CROPS AS AFFECTED BY THE EC OF THE EXTERNAL NUTRIENT SOLUTION AND BY HUMIDITY

In a series of experiments effects of EC values in the root environment and differences in climatic conditions were studied in relation to the uptake of cations. Tomato, cucumber and sweet pepper were used as test crops. Differences with EC values were realised by the addition of various concentrations of nutrients, whereby the mutual ratios between the nutrients were kept constant. Differences of climatic conditions were realised by ventilation, heating, screening regimes and evaporation of water from open water basins. For all crops a spring and a fall grown crop were incorporated in the study. The uptake of the cations was determined by tissue samples. Young fully grown leaves and ripe fruits were sampled and analysed systematically. Accidentally, old leaves and tops were sampled and analysed, while in some cases the fruits were separated in a proximal part and a distal part. The K concentration in the plant tissues was increased and the Ca concentration was decreased by an increasing EC in the external solution. The Mg concentration in the plant tissues was affected less evidently by an increased EC. The overall effect of the humid climate was a decrease of the K and Mg concentrations in the leaves and a small increase of the Ca concentration. The K, Ca as well the Mg concentrations in the fruits were increased by the high humidity in the greenhouse. However, these effects were not of the same size as occurred with the EC and were not consistent for all crops. The average Ca concentration in the distal end of the tomato fruits was 40% lower than in the proximal part; for sweet pepper this difference was only 10%. Increased nutrient concentrations in equal ratios, to enhance the EC in the external solution, had only slight effects on the uptake of cations in comparison with the effects of nutrient concentrations realised by different ratios in the external solution at an equal EC value. In this way it was shown that great differences can occur in the cation uptake by plants, while the cation concentrations in the external solution were equal. Therefore, with the interpretation of analytical data of cation concentrations in the external solution in substrate systems, beside the concentration at such, especially the relation to the other nutrient cations should be seriously taken into account. Guidelines for interpretation are discussed.