Articles
SOIL CULTIVATION AND WATER SUPPLY
Soil cultivation
Bitter pit of apples is presumed to be a physiological disturbance caused by excessive potassium supply and too little supply of calcium to the trees.
Numerous soil samples in Lower Rhineland apple orchards showed that the upper 15 cm of the soil under the trees contain more potassium than the deeper soil layers.
Because of replacing mechanical soil management of former times by application of herbicides in modern soil treatment tree roots occupied the upper soil layer.
As leaf samples indicate the trees take up potassium in excess and neglect to take up calcium as an effect of antagonism between potassium and calcium.
To destroy the root system down to a depth of 15–18 cm an orchard of Cox’s Orange Pippin was worked by a rotavator between May and July one to four times.
The control plot was left unworked with a slight growth of weeds.
The treatments included are given in table 1. As it is shown in table 2 more frequent working of the soil resulted in a decrease of potassium and an increase of calcium values.
A clear trend of the K+Mg/Ca ratio confirms these findings.
When we take the average of 50 Lower Rhineland commercial orchards where tree rows were treated with herbicides leaf analysis indicated a K+Mg/Ca ratio of 2,47, corresponding to the one time working in July.
By rotavating four times the occurence of bitter pit was 0 % as compared with 20–27 % bitter pit in the other plots.
Soil working in May gave the best response, the July treatment almost not at all.
In agreement with Pouwer we explain this phenomenon as follows: Potassium uptake by the trees mainly takes place in April/May and soil working during this time partly prevents the uptake of potassium by the roots.
The results of this trial are published in "Gartenbauliche Versuchsberichte 1970" of Landwirtschaftskammer Rheinland, Bonn.
The growers in our area make use of these experimental results and are now working