Interactive effects of air humidity, calcium and phosphate on blossom‐end rot, leaf deformation, production and nutrient contents of tomato

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Abstract
Blossom‐end rot is not the result of a single factor, but from the interaction of several factors. To prove this and to get information on how to lower the detrimental effect of blossom‐end rot, a multifactorial trial was conducted. Tomato plants, grown in rockwool in a circulating system, were fed with 0.75, 1.25, and 1.75 mM phosphate (P) and two calcium (Ca) levels resulting in 4.0 and 11.2 mM Ca in the leachate. Two air humidity levels were maintained. The low Ca, P, and humidity resulted in higher levels of blossom‐end rot than the higher levels of these factors. The increasing effect of low P on blossom‐end rot could be the result of the fact that at low P, ammonium (NH4) addition was higher than at high P, because at low P, the pH tended to increase and pH control was done by adding NH4. However, it is possible that an effect of P remains. The combination of the factors at the low levels gave rise to 59% blossom‐end rot. In this treatment, plants suffered in course of time from severe leaf deformation and die‐back of the growing point. Therefore, the experiment had to be stopped earlier than planned. The cause of the deformation was the high amount of blossom‐end rot. Plants were not able to store assimilates in fruits. To avoid blossom‐end rot, growers have to maintain the P concentration in the root environment of at least 1.7 mM and a Ca concentration of 8 to 9 mM. Air humidity should be kept high.