Summary
Previous work has suggested that the presence of P32 in fertilizers inhibits the uptake of the applied phosphate from the soil by plants, and also that if the applied phosphate is not incorporated uniformly in the soil there will be preferential uptake from regions of low specific activity. This made it desirable to determine the effect of P32-level on phosphate uptake and the determination ofL-values in pot experiments in which the labelled phosphate source is added as discrete particles of the phosphate form of an anion-exchange resin.
Increasing the level of P32 from 0.05 to 1.25 mo per gram of phosphorus in the added phosphate did not have a significant effect on the fresh weight, dry weight or total phosphorus uptake of the ryegrass crop. The measuredL-value showed a significant increase, about 15 per cent for a five-fold increase in P32 level, on each of the four soil types used, as would be expected if P32 depressed the uptake of labelled fertilizer phosphate.
Although a significant effect of P32 was observed this does not invalidate a comparison of soils with respect toL-value.
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Larsen, S., Cooke, I.J. The influence of radioactive phosphate level on the absorption of phosphate by plants and on the determination of labile soil phosphate. Plant Soil 14, 43–48 (1961). https://doi.org/10.1007/BF01343768
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DOI: https://doi.org/10.1007/BF01343768