Quote:Two methods help us with the fine-tuning of plant nutrition:leaf analysis and foliar
fertilization.

Modern Guidelines on Fruit Tree Nutrition

Wolfgang Drahorad
South Tyrolean Advisory Service for Fruit- and Wine-Growing
Terlan, Italy

Presented at the 42ndAnnual IDFTA Conference, February 20-24, 1999, Hamilton, Ontario,
Canada.

In the South Tyrolean fruit industry plant nutrition is considered a means to achieve the following
primary objectives:

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high and regular yields
good internal quality (storage potential, flavor, taste, firmness)
external quality (fruit size, color, texture)
little leaching

In order to achieve these objectives we make use of the following knowledge and techniques:

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knowledge of the nutrient losses through crop and soil
nitrogen balance in the soils
results of trials on fertilization
soil, foliar and fruit analyses

The nutrient requirements of the crop are determined from the nutrient balance in the soil under
our conditions. From fruit analyses and the mean production per hectare of 45 metric tons (MT)/
ha or 45 bins/acre we know the amount of nutrients taken up from the soil each year. This is an
important parameter for us because our fertilizer program is based on it (Table 1).

If the nutrient supply in the soil is within the optimum range (class C) according to the soil analyses
and our assessment, we recommend supplying an amount of nutrients which is slightly higher than
that taken up by the crop (Table 2).

If there is a slight deficiency of these elements (class B), the nutrient supply is increased by 50%.
On the contrary, if there is a slight surplus of nutrients in the soil (class D), the quantities are
reduced by 50%. In case of a severe shortage, the fertilizer quantities are doubled. With a
considerable surplus, a suspension of fertilization for several years is recommended.

In plant nutrition the health and the quality of the soil also play an important part. This applies
especially to mobile elements like nitrogen, potassium and the trace element boron which tend to
leach out.

In the South Tyrolean fruit growing region, approximately 80% of the acreage is on sandy loam
soils or loamy sand of light to medium texture. The clay content varies between 8 and 15%. Soils

containing high amounts of clay are rare in our region. Near the rivers there are mainly sandy soils.
In general our orchard soils are low in calcium, the pH ranges from 5.5-6.5.

Only about 20% of our orchards are situated on dolomite sediments. The calcium content and the
pH value are accordingly higher (pH 7-8%). The South Tyrolean orchards are well supplied with
humus (organic matter) because for decades it has been the practice to mulch the grass and all the
organic parts of the trees, including leaves and the wood prunings. The humus content is within an
optimum range of 3-5% and tends to increase.

The nitrogen level in the soils is generally well balanced, since the losses and the applications are
in equilibrium in the long run. We adopted for our conditions the method developed by the
German researcher F. Weller (Table 3).Of course, this balance is valid only for average soils
with a humus content of approximately 3-4%. If on such soils nitrogen applications are
suspended for some time, symptoms of N-deficiency such as small, yellow leaves, small fruits
and stunted growth appear.

In soils rich in humus, e.g., in the lower elevations at the bottom of the valley, the N-balance is
certainly positive. This means that the nitrogen supply through the breakdown of humus is higher
than the losses through leaching and the crop. In such cases nitrogen fertilization is not advised.
Practical proof of this is that there are quite a number of orchards where no nitrogen has been
applied for many years with good crops and no deficiency symptoms.

On the other hand, the rare, very sandy soils which are low in humus have a negative N-balance,
that is, their nitrogen requirements are higher than the natural supply.In thiscase it is often necessary
to apply higher amounts of nitrogen than those which are used up by the crop.

Theories are quite uselessunless they are confirmed by trials, practical experiences and observations.
The Experiment Station Laimburg has carried out a trial on the application of increasing rates of
fertilizers over a period of 17 years (Table 4). The results showed clearly that an increase in the
application of nitrogen beyond the rates of 60 kg/ha N (53 lbs/acre N) does not lead to higher
returns. This has contributed materially to a sound scientific back-up of the recommendations.

SOIL ANALYSIS
Soil analysis is essential for the orchardist and the adviser, since it supplies the basic data on the
soil and its nutrient status. We test the soil for pH value, humus content, soil type and calcium
level. Phosphorus, potassium and magnesium levels are determined in accordance with the
German LUFAResearch Laboratories.

Soil analyses are recommended for new plantings and young orchards. In the Integrated Production
(IP) program it is mandatory to carry out a soil analysis within the first years. In bearing orchards a
soil test is required every 5 years. Our two laboratories for soil analyses test approximately 3,000
soil samples every year for the fruit growers. The trend is increasing.

As a specialist in plant nutrition I assess hundreds of soil analyses every year and work out the
fertilization requirements. In my experience in more than half the cases a significant reduction of
fertilizer input can be recommended in comparison with the original fertilizer programs of the
operations.This saves money, improves the internal and external quality of the fruits and safeguards

the soil and the water against toxic nitrates. The costof US$40per analysisisnegligible in comparison
with its advantages.

We did not have much use for the traditional leaf analyses which were usually performed in mid-
summer.This is because
•results of the analyses arrived too late to allow major corrections through fertilization during
the vegetative period
•leaf analyses can be utilized only to a certain extent for fertilizer programs in the following year
•growers were not ready to have leaf analyses made in the summer until shortly before harvest

EARLY LEAF ANALYSES
For these reasons we had been thinking of a new, earlier time of leaf analyses, soon after bloom.
From 1993 onward the Research Station Laimburg launched an intensive program of leaf analyses
carried out in many orchards in order to determine the nutrient level in the leaves in the course of
the vegetative period. From these data the optimum range of nutrient levelswas developed, starting
from full bloom. Each element has its own typical curve, as is shown in the graphs (Figures 1, 2, 3).

This system allows us to make leaf analyses during the whole period of vegetative growth. The
results are compared with the optimum values of the curve at the time of sampling. A result above
the upper curve indicates a nutrient surplus,a result below the lower curve a nutrient deficit. However,
the curves shown above are not intended to remain static; they are periodically adjusted with new
findings.

Early leaf analysis has many advantages:
•At the time of thehighest nutrient requirements (after bloom) it is important to determine a
nutrient excess or deficiency.
•Inspringtheconditionsarefrequentlyunfavorablefornutrienttake-up(frost,lowsoil
temperature, waterlogging).
•An imbalance of the nutrient levels in the early vegetative period has negative effects on fruit
set, bud formation and differentiation for next season and fruit quality.
•In case of a nutrient deficiency, a fast soluble mineral fertilizer or foliar fertilizer can be applied
in time.

As we have had some problems with the availability of nutrients and trace elements, we have
established a monitoring system of early leaf analyses in numerous trial orchards. With this system
we can observe and analyze the characteristics of nutrient uptake during the season which are
influenced by the meteorological conditions. On the basis of this we can work out our
recommendations.

For example, in the cold spring of 1997, with frequent frosts, in numerous orchards the nitrogen
concentration in the leaves was low after bloom. Through the frost irrigation much nitrogen was
leached out and the low soil temperatures impeded the uptake of nitrogen. In this case we
recommended foliar urea sprays because they are rapidly absorbed. Among the trace elements,
manganese and boron seem to be very important for healthy development of the leaves. If our
monitoring system should detect many cases of deficiencies of these two elements, we could
immediately warn our orchardists to apply foliar manganese or boron sprays.