Componenten van het fosfaat in de grond welke betrokken zijn bij de fosfaatvoorziening van de plant

The phosphate supply of a plant largely depends on the amount of phosphate which can be released from phosphate reserves into the soil solution. The behaviour of exchangeable soil phosphate and the best method of estimating the isotopically exchangeable fraction was studied in pot experiments with oats and experiments with soil suspensions.

The kinetics of phosphate ions in soil suspensions were discussed. The results of the experiments indicated the course of the exchange of phosphate ions between the solution and the solid reserve. The isotopically exchangeable soil phosphate appeared to be heterogeneous in composition.

The quantity of isotopically exchangeable soil phosphate (L- and E-values) was calculated on the assumption that isotopic balance had been reached in the experiments at least for a certain part of the soil phosphate. For the L-value (determined in pot experiments) the consequences were studied of a lack of equilibrium.

Finally the quantities of phosphate absorbed by oat plants were compared with those withdrawn by ion exchangers from soil suspensions (of a soil with the same phosphate reserve).