Electro-ultrafiltration of aqueous soil suspension with simultaneously varying temperature and voltage
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The procedure of electro-ultrafiltration (EUF) with simultaneously varying voltage and temperature for the determination of nutrient fractions in soil as well as for the characterization of important soil properties such as kind of clay, content of K-selective clay minerals, of CaCO3etc. is described. The interpretation of the EUF-N, EUF-P and EUF-K fractions is discussed in detail with regard to their availabilities. Moreover the influence of soil properties and soil management on the EUF nutrient fractions is discussed.
For characterization of the EUF values needed for optimum plant nutrition, it is suggested to combine the EUF values at 20°C and 200 V on the one hand (easily available fraction) and the EUF values at 80°C and 400 V on the other (nutrient reserves). The higher, in fact, the nutrient contents at 80°C and 400 V are the lower can be the EUF values at 20°C and 200 V. In contrast to conventional methods of soil analysis, the nutrient contents determined by EUF are expressed in mg/100 g soil/time unit of desorption (min) at given temperature and voltage.
The EUF procedure proved highly advantageous for an assessment of the fertilizer requirements of soils as this method allows for the determination of soil properties such as kind of clay, content of K-selective clay minerals, of CaCO3 and of easily desorbable heavy metals in one single operation. These soil properties play a decisive role in the sorption of K and P.
Key wordsFertilizer requirement Nutrient availability Nutrient fractions Nutrient reserves Soil analysis Soil solution
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