'n Vergelykende ondersoek van 'n potkultuurmetode en sekere ander metodes vir die bepaling van toeganklike plantvoedingstowwe in die grond

Abstract

An attempt was made to correlate results obtained with biological and chemical methods to determine the availability of N, P and Kin different soil types. The pot culture method, in its present form, apparently is the most reliable to determine the availability of plant nutrients in the soil. Different cultivated plants react differently to the addition of N and Pin pot culture which may probably be ascribed to the so-called feeding power of plants and/or the interaction between pot size, soil mass and duration of experimental period. The availability of soil air and duration of experimental period show a pronounced influence on the results obtained with the pot culture method. The question therefore arises to what extent the results obtained with this method, in its present form, are transferable to field conditions. The dehydrogenase method, as compared with the pot culture method, gives an exaggeration of deficiency of available N in at least loamy soil, while deficiency of available Pin loam, sand and clay is underestimated. The dehydrogenase method also underestimates the deficiency of available Kin at least sandy soil. The methods of Morgan and Schuffelen, Muller en van Schouwenburg are apparently useful to determine available Pin sandy and loamy soil but not in clay, while they are apparently also useful to determine available Kin sandy soil but not in loam and clay. The method of Bray is apparently useful to determine available P in sand, loam and clay, while it is apparently also useful to

determine available Kin at least sand and clay. All three chemical methods mentioned above apparently underestimate the availability of N for maize plants in sand, loam and clay.