Starting from a very high fertilizer input we have now, after years of educational work, come very
close to the actual nutrient rates required by a modern intensive planting. In spite of the reduced
nutrient supply the yields are still increasing in our fruit growing area and the remarkable thing is
that fruit quality also improves, especially taste and storage life. Of course, this practice sometimes
takes us close to the lower limits, even with our fertile soils. Here we can easily slide into a slight
nutrient deficiency. This situation obviously requires a good sense of the correct nutrient rates.

Two methods help us with the fine-tuning of plant nutrition:

leaf analysis and foliar fertilization.

FOLIAR FERTILIZATION
Foliar fertilization is used for fine-tuning as
•a curative measure if deficiency symptoms occur
•a supplement to soil applications (if the uptake through the roots is impeded)
•a prevention of physiological disorders (leaf drop, bitter pit, etc.)
•a method to increase the reserves in the plants

We recommend the application of magnesium as magnesium sulfate (7-15 kg/ha = 6.2-13.4 lbs/
acre) or as magnesium nitrate (4.5-6 kg/ha = 3.6-5.3 lbs/acre) in the following cases: 1) a magnesium
deficiency (leaf symptoms or indicated by a leaf analysis) and 2) aspreventive treatmentson Golden
Delicious and Gala if leaf spots or drop occur or if there is an accumulation of risk factors.

The new varieties Gala, Braeburn, Fuji and Pink Lady, but also Golden Delicious, are rather
susceptible to magnesium and manganese deficiency and react with poor leaf development and
spotted leaves. In these cases we recommend 2-3 treatments with manganese sulfate 3 kg/ha (2.7 lbs/
acre) or Mantrac (Phosyn) 0.5 kg/ha (0.4 lbs/acre).

Boron fertilizers are readily absorbed by the leaves and transported to other parts of the plant. In
order to ensure above all a good function of blossom organs, which is important for pollination, we
recommend 2-3 boron applications (Borax 2.5 kg/ha = 2.2 lbs/acre or Solubor 1.5 kg/ha = 1.3 lbs/
acre) from pre-bloom onwards. We usually mix boron with scab pesticides. Through these widely
used treatments our light soils, which are low in boron by nature, receive annually a basic supply of
this trace element.

Phosphorusand potassium are normally not applied as foliar sprays, iron and zinc only in exceptional
cases.

FOLIAR CALCIUM
As a calcium fertilizer for preventing bitter pit and other physiological disorders, calcium
chloride as a salt or in a soluble form has proven effective. Depending on the variety, the crop
and the risk of bitter pit we recommend a range of calcium sprays (Table 7).

Factors to consider with calcium applications include:
•calcium chloride and, in case of a nitrogen deficit, calcium nitrate are the most effective foliar
fertilizers
•begin sprays from 70 g fruit weight onwards; preharvest treatments are most effective
•calcium sprays can be delivered with fungicides, with low water volumes and through over-tree
irrigation
•calcium chloride has no negative effect on the blush, fruit size and photosynthesis

If bitter pit pressure is very high, calcium applications alone can only diminish bitter pit incidence,
not eliminate it.

FERTIGATION
Also in our fruit growing region drip irrigation systems are advancing, partially in combination
with over-tree irrigation. This allows a fertilization technique known as fertigation. We know of
the Dutch experiences with fertigation, where it resulted in increased growth, more flower buds
and higher initial yields, especially in young orchards. In the trials carried out at the Research
Station Laimburg, we also noticed somewhat increased growth and crops in the fertigation plots
but not to such an extent as recorded in the Dutch experience. The fertigation plots showed a
light increased tree growth in the first year (Figure 5).

However, it is not easy to discern how much of this is due to the regular irrigation and how much to
the regular supply of soluble fertilizers. The cumulative yields over 5 years for Gala were also
higher in the fertigation plots (Figure 6).

However, the increase in yields was not so high in comparison with the plots with broadcast
application of different fertilizers as to justify the additional costs of drip irrigation since over-tree
sprinklers are indispensable for frost irrigation. Our Advisory Service recommends drip irrigation
only on elevated sites which are free of frost. In these sites this new technique is a practical method
of distributing nutrients. The market offers a multitude of rather expensive soluble mixed fertilizers
in various compositions. For economic reasons we prefer to use fertilizers containing only one or
two elements, like calcium nitrate, urea, ammonium monophosphate, potassium nitrate, potassium
sulfate and others.

CONCLUSIONS
Knowledge and modern analytical techniques help us find the right nutrient need for each
orchard. Applying these techniques in the practice can improve fruit quality, save money and
protect the environment.

Table 1.Nutrient needs of a crop of 45 MT/ha.

Nutrient

kg/ha

lbs/acre

N
P2O5
K2O
CaO
MgO

15.7-22.5
9.9
54-72
3.3
3.6

14-20
8.8
48-64
3
3.2

Table 2.Suggested fertilizer rates with optimum soil
nutrient level for a Golden Delicious crop of 45 MT/ha in
South Tyrol, Italy.

Fertilizer

kg/ha

lbs/acre

P
K
Mg
B

10-20 kg P2O5/ha
60-100 kg K2O/ha
20-30 kg MgO/ha
0.5-0.7 kg B/ha

8.9-17.8 lbs/acre
53-89 lbs/acre
17.8-26.7 lbs/acre
0.45-0.65 lbs/acre

Table 3.Example of an orchard nitrogen balance (based on F. Weller).

Input

lbs/acre

kg/ha

Loss

lbs/acre

kg/ha

Rainfall
Biol. binding
Grass mulch
Pruned wood

17.8
17.8
178
26.7

20
20
200
30

gaseous loss
leaching
grass
orchard uptake

17.8
17.8
178
26.7

20
20
200
30

Totals

241

270

241

270

Table 4.Cumulative crops 1972-1989 from N-fertilization trial at the Experiment Station
Laimburg.

Treatment

60 kg/ha N
(53 lbs/acre)

120 kg/ha N
(107 lbs/acre)

Variety

Control

Annual yield

Yield change

Golden Delicious

45 t/ha

plus 4.2%

minus 0.1%

Rome Beauty

95 t/ha

plus 13.2%

plus 17%