MINERAL NUTRITION AND PHYSIOLOGICAL FRUIT DISORDERS IN THE NIEDERELBE REGION OF GERMANY

Surveys were carried out in 1972, 1976 and 1978 on different orchards of Cox's Orange Pippin apple. Leaf samples were collected for mineral analysis and fruit samples for determination of physiological disorders after storage in air at 2.5 °C until January. In 1972, when rainfall was near to average, only the percentage bitter pit correlated positively with the potassium content of the leaves whereas, in the very dry year of 1976, the incidences of both bitter pit and internal breakdown were more severe with increasing leaf potassium. In the wet year of 1978, positive correlations were established between leaf potassium content and the incidence of bitter pit in both air and controlled atmosphere (CA) storage. The coefficient of correlation was, however, higher for the CA-stored fruit probably because, under CA conditions, overall bitter pit levels were about 50 per cent lower than in air storage and the variability between orchards in the incidence of the disorder was reduced.

Leaf calcium concentrations were negatively correlated with bitter pit in the wet years of 1972 and 1978 only. Bitter pit was also negatively correlated with the nitrogen content of the leaves in two of the three years while breakdown was significantly correlated with leaf nitrogen in one year only.

Low incidences of bitter pit were related to the frequency with which calcium sprays were applied by the growers but there was very little relationship between soil pH and bitter pit.

Due to the inconsistency of the correlations, which were obtained in the different years, between physiological disorders and the concentration in the leaves of mineral nutrients other than potassium, the investigations were expanded from 1978 onwards to include analysis of the fruit as well.

It is evident, from some 1000 commercial soil tests on fruit farms in the region, that 50 per cent of the orchards have a requirement for liming, shown by pH values below 5.5. Also that 90 per cent of the orchard soils contain levels of potassium which are excessive as regards susceptibility to physiological disorders of apple fruit. Magnesium deficiency symptoms occur only on the light diluvial soils, especially where the soils are of high potassium content. Manganese deficiency symptoms are frequently seen in orchards on clay soils which have a natural pH higher than 6.0 in areas which, until recently, have been reached by high floods of the Elbe river.