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Abstract Between 10 and 40% of P was lost during perchloric acid digestion of NaHCO 3 soil extracts for measurement of organic P. This observation was confirmed by 32 P tracer experiments. Addition of MgCl 2 prevented P loss, reduced variability of replicate determinations and ensured virtually 100% recovery of P added to NaHCO 3 solution and NaHCO 3 soil extracts before digestion. Losses were due both to P volatilisation and conversion of P to forms other than ortho‐P in the digestion mixture.
Brookes et al. (1981) studied this question.