Articles
EFFECT OF BORON FERTILIZATION ON YIELD AND FRUIT QUALITY OF ‘ELSTAR’ AND ‘SAMPION’ APPLE CULTIVARS
The investigation was carried out during the period 1994–1996. Trees of ‘Elstar’ and ‘Sampion’ cultivars were grafted on M.26 rootstock and planted on sandy-loam soil with low pH, low organic matter and low B concentration.
Three B treatments were applied:(i) B application to the soil at a rate of 2kg B ha-1 as Bortrac (16% B as a boric acid), (ii) B sprayed before bloom at a rate of 0.67kg B/ha/spray applied in the stage of green and pink bud and beginning flowering (total rate of 2.01 kg B/ha/year), (iii) B sprayed after bloom at a rate of 0.67kg B ha-1 with the first treatment applied at petal fall and the next two at 2 week intervals (total rate of 2.01 kg B/ha/year). Trees without B fertilization served as control plots.
Boron increased ‘Elstar’ and ‘Sampion’ fruit set and yield only when sprayed after bloom, however in some years of the study this treatment decreased fruit weight.
Boron spraying after bloom increased also Ca concentration in fruits which resulted in increased apple firmness after storage and decreased sensitivity to bitter pit and internal breakdown for ‘Sampion’ apples.
In contrast, apples of the ‘Elstar’ cultivar showed decreased storage quality when sprayed with B after bloom, suggesting that ‘Elstar’ apples are more sensitive to B excess than those of ‘Sampion’ cultivar.
Although both spraying with B after bloom and application of B to the soil increased B and Ca concentrations in apples, the latter treatment did not affect yield, fruit harvest and post-harvest quality.
Results showed that the requirement of apple trees for B is cultivar dependent and the method and time of B application could be critical for efficient B use by apple trees.