K fixation test by soil.
This method determines the amount of soil K fixation potential associated with illitic clay soils. Potassium is added to soil, then dried and incubated for seven days. Potassium concentration is determined using atomic emission (AES), absorption spectrometry (AAS) and inductively Coupled Plasma (ICP) instrumentation and fixation capacity calculated based on the amount of K recovered. Generally, the method is reproducible within ± 7% K on a given soil, or 3 – 5% on a soil K fixation basis.