|Authors: ||C. Sonneveld, W. Voogt|
The availability of nutrients to plants in a substrate system can mostly not solely be predicted by the analytical data of a sample gathered at random from the root environment.
Besides the chemical composition of the substrate solution or extract, a large number of other parameters are important for an optimal management of the nutrient supply in substrates, such as the concentration and the mutual ratios of the ions in the nutrient solution supplied and in the drainage water, the irrigation method, and the pH, volume and shape of the substrate.
In most substrate systems nutrients and other salts are unequally distributed in the root environment.
Then the place where the sample is gathered is very important and will strongly affect the results of the analytical data and their interpretation.
Guidelines will be given for sampling and interpretation of analytical data depending on growing conditions and extraction methods.
In hydroponic systems the interpretation of data of routine samples seems to be rather simple, for the solution samples gathered for the analysis directly reflect the composition of the solution in the plant root environment.
Also for some substrates the solution from the root environment is used for analysis.
This is for example the case with rockwool and foam slabs.
In other cases the substrate is sampled and extracted, and the determinations are carried out in the extract.
If water is used as an extractant, the data of EC measurements should be converted to substrate solution values.
This is also possible for nutrient concentrations, but not necessary.
In the paper presented it is emphasized that the interpretation of the analytical data of samples gathered from the root environment of the growing system should be integrated with the conditions in the system considered.
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