Articles
A STRATEGY TO PREVENT BITTER PIT INCIDENCE IN ORGANIC APPLE GROWING BY COMBINING AN EARLY RISK PREDICTION ON THE BASIS OF FRUITLETS ANALYSIS AND SPECIFICALLY ADAPTED SOIL MANAGEMENT
Our investigations aim to improve the strategy to prevent bitter pit by an early prediction method and also by specifically adapted soil management methods.
The studies described are based on a earlier field study where the best early prediction of Ca-nutrition of the fruits and bitter pit incidence was the K- and Ca-concentrations of fruitlets at T-stage.
In 1996 we tested in a commercial organic orchard different soil management methods to improve Ca-uptake of the fruit.
Relative to trees grown with a living sod in the tree strip (i) sea algae powder, (ii) horn-chips, (iii) mature compost and (iv) tillage treatments could increase the amount of Ca in the soil solution of the topsoil.
In 1997 the tillage and application of sea algae powder or horn chips (control was a living sod) were applied again in 3 organic orchards (cv. ‘Boskoop’ and ‘Maigold’). The results confirmed the potential to predict the risk of bitter pit and the K:Ca ratio in ripe fruits on the basis of the Ca and K concentrations in the fruitlets at T-stage.
A K:Ca ratio above 5.8 indicated considerable risk of subsequent bitter pit development.
Also soil Ca and K concentrations correlated to bitter pit incidence when using the ratio between the ammonium acetate-soluble and the water-soluble fraction.
The direct treatment effects on soil, leaf and fruit parameters indicated a trend to increased availability of Ca and Nmin in the soil and of Ca-uptake of the fruits after application of sea algae powder or horn chips.