THE APPLICATION OF MANGANESE IN NUTRIENT SOLUTIONS FOR TOMATOES GROWN IN A RECIRCULATING SYSTEM

The results showed that at the high pH level the manganese content of the recirculating nutrient solution decreased sharply after several months. This was not the case at the low pH level. The results of the crop analyses were in good agreement with this. The manganese contents of the leaves were found to be much higher at the low pH than at the high pH level. Although the manganese contents in the nutrient solution became very low at the high pH level, the crop could still take up sufficient manganese and consequently differences in yield between the treatment were not found. The manganese content of the nutrient solution is apparently not always a reliable measure of the manganese uptake by the crop. Crop analyses may sometimes give a better indication. If necessary, the press sap of the petioles could be used for a quick test.

It has been calculated from the results that for tomatoes grown in a nutrient solution at a high pH level, a rate of 1 mol manganese per 600 mol nitrogen would be required. The usage of manganese is more efficient at a low pH in which case a ratio of 1 mol manganese per 1,000 to 1,500 mol nitrogen might be sufficient. If the manganese uptake is monitored with the aid of petiole press sap, about 0.1 mmol.1^-1 manganese should be present in young, fully-grown leaves.

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