Calcium deficiency of ‘Cox's Orange’ apple trees during the fruit growth period

In a pot experiment with apple trees, cultivar ‘Cox's Orange’, Ca was omitted in the nutrient solution for periods of different length. Trees lacking Ca in the latest $\text{2}\text{3}$ of the growth period contained 42 mg kg^?1 Ca in the fruits, which is 21% below control. In the bulked sample, average size of fruits was not considerably affected, but the distribution of small and large fruits changed toward more smaller fruits. Concommitantly, bitter pit was reduced compared to the control.Sufficient K supply (1.20–1.70% K in leaf dry matter) given to trees receiving high Ca supply depressed Ca concentration in the fruits to 41 mg kg^?1, which is 23% below control. Average fruit size was not significantly changed, but the distribution was towards larger fruits. Under these circumstances bitter pit was increased. Ca deficiency, caused either by omission of Ca or competition between K and Ca, increased fruit rot, russeting and cracks on the fruits. Short term variations in Ca levels were not seen to produce any measurable response.