Determination of K forms in K-fertilized soils by electro-ultrafiltration

✍ Scribed by B. Rubio; F. Gil-Sotres

• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 619 KB
• Volume: 180
• Category: Article
• ISSN: 0032-079X
• DOI: 10.1007/bf00015314

✦ Synopsis

We confirmed the suitability of electro-ultrafiltration (EUF) for (a) determination of the distribution of potassium fertilizer among the various forms of potassium in soils with a predominance of micaceous minerals in their clay fraction, and (b) investigated the effects of the degree of openness of the dominant micaceous mineral and of incubation time on the kinetics of the EUF extraction of K from these soils.

Samples of illitic, mixed-layer and vermiculitic soils from Galicia (N.W. Spain) were incubated at field capacity for 450 days with 0 (blank), 5,15 or 25 mg K (as KC1) per 100 g dry soil. After 1, 30, 150 and 450 days, subsamples were removed and repeatedly extracted using electro-ultrafiltration at low (20 o C/200 V) and then high (80 o C/400 V) temperature/voltage (6 and 10 five-minute extractions, respectively). Five different "pools" of K were identified: solution K (Ks), surface and internal K (collectively, Kp), slowly exchangeable K (Ke) and non-exchangeable K (Ki). The effects of increasing the incubation time depended on the dominant clay mineralogy: after 450 days, the K added to illitic soils was mostly solution K, whereas that added to vermiculitic soils was mostly internal K.

For both low and high temperature/voltage EUF experiments, the extraction-time data were best fitted by the Elovich equation (extracted K = a + b In t). The kinetic coefficient b depended on the incubation time and dominant clay mineral, and for given soil and incubation time increased linearly with the dose of added K.