Experiences with the modified Baker-Amacher soil extraction procedure in Hungary

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.