measurement methods of soil, water, plant and fruit, in berry ... - NJF

SAMPLING, ANALYSIS AND INTERPRETATION
OF NUTRIENTS LEVELS IN APPLES
Thomas Olsson
AnalyCen Nordic AB
Box 9024
291 09 KRISTIANSTAD
email thomas.olsson@analycen.se
Background
Knowledge of the nutrient status in apples during different growing stages is of great
importance since it might answer questions regarding malnutrition, fertilisation strategy
sensory quality aspects and storability. Since the final amount of analysed sample is very
small (few grams) much care must be taken on sampling and further subsampling.
What parameters causes variation?
Representative samples from a given field with one variety must include variations such as
topography, soil chemistry, sunlight as well as water exposure. All these parameters will
effect nutrient uptake and hence effect analytical results. Another approach is to sample
different subfields with uniform conditions and analyse separately, unfortunately at higher
analytical costs. If a field is very heterogeneous regarding soil chemistry (ie different soil
types) this approach is how ever recommended.
Number of individuals.
The number of individuals is a compromise between statistical variations of nutrient content
between individual apples and practical handling of the samples regarding transport and
analytical costs. At earlier growing stages (fruitlets) nutrient variation in individuals vary
more than at more matured stages and hence greater number of individuals should be
analysed. A commonly accepted role of thumb is 40 individuals for fruitlets and 20
individuals for fruits.
Subsampling
At the laboratory the sample has to be subsampled into a smaller portion in order to be able to
handle it in the analytical equipment. From each individual two opposite slides will be taken
and put in a blender. The slides will then be thoroughly mixed to homogeneous slurry. For
apples with low water content water has to be added during mixing. The sample is then ready
for further analysis.
Digestion
When analysing for total content of nutrients organic matter has to be removed without any
loss of nutrients. Different methods are used involving dry ashing, acid digestion, microwave
supported acid digestion. We are using closed vessels microwave supported acid digestion.
The method gives short digestion times and losses can be avoided. The amount of samples
actually analysed is from 3 – 20 grams depending on method used.
Measurement
The final detection and quantification of the nutrients are carried out with means of ICP-
OES, ICP-MS and for nitrogen automatic distillation.
Uncertainty