The Baker and Amacher equilibrant and extractant with PO4-P addition seems
to be useful for measuring not only K and Mg requirements but also for test
ing P adsorption of soils as single point isotherms. The correlations betwe
en CaCl2-P (readily desorbed P) and mBA dP (adsorbed P) quantities showed d
ifferent P adsorption hysteresis in soils. The trend of adsorbed P amounts,
measured in soils from long-term fertiliser experiments, strengthened our
early experiences. Differences of P,K and Mg sorptions were measured in buf
fered and unbuffered mBA equilibrants. While sorption in the unbuffered mBA
equilibrant is theoretically closer to field processes, the K and Mg requi
rements in unbuffered mBA seem to be overestimated. This has to be taken in
to account during calibration.