Behaviour of carrier‐free phosphorus‐32 in natural soils in relation to the measurement of labile soil phosphorus

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Abstract
The process of isotopic equilibration in perfused crumbs from five soils has been studied by following changes in the specific activity of the perfusates. The soils vary considerably in the times required for isotopic equilibrium with phosphate ions in the perfusate and in the penetration of labelled phosphate into the soil crumbs.A 55% drop in isotopic dilution was brought about by a reduction from 23° to 3° of the temperature at which crumbs from one soil type were equilibrated in a static system. This temperature drop doubled the time required to achieve uniform distribution of 32P.It is concluded that the rate of isotopic equilibration in pot experiments will be slow and may be limited in certain soils by the slow rate of redistribution on a micro scale of unevenly applied 32P.
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