L'ho trovato in inglese, vedi http://www.cespevi.it/idri/pardox04.pdf
Metodi per la determinazione delle caratteristiche fisiche e chimiche dei substrati
Analisi dell’estratto acquoso
Prelievo ed analisi della soluzione nutritiva nel substrato (aspirazione, centrifugazione, squeeze)
e c'è la stessa foto di qui: http://www.ces.ncsu.edu/depts/hort/floriculture/plugs/gttest...
The squeeze method provides a simpler, faster, and more representa- tive method of sampling substrate for nutrient analysis than the saturated me- dia extract (SME) or 2 water : 1 substrate methods. This method is fast because it is not necessary to dry the substrate as in the 2:1 method. The resulting solu- tion may be used immediately for pH, EC, and specific nutrient determinations. The “Squeeze” is easy because once the plug is removed from the tray all that is necessary is to squeeze the solution from the substrate. It is more representative of the nutrient situation experienced by the root than the other two methods be- cause no subjective step is involved in adding the correct amount of water dur- ing extraction.