E-VALUEExpected Value
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4, and also for experiments in which E-values are determined after only short exposure times of the isotope to the soil (Fig.
E-values determined (see below) from the fraction A solutions correspond to the `standard' E-value method adopted by many researchers, though the time of incubation with isotope can vary from 1 min to >3 days.
The theory underlying the concept of E-values using the standard methodology has been described by many researchers (McAuliffe et al.
1, it was therefore anticipated that problems might be expected in the determination of E-values for the soils KO, PG, QL, HAS, and KT.
Potential interferences in the determination of P E-values
There are several reasons advanced to explain the difficulty in determining realistic E-values for soils that have a high P sorption capacity and these are discussed below.
1994) have speculated that overestimation of E-values may be due to the presence of significant quantities of soluble silicate in the soil, which reacts with the molybdate reagent to form a blue complex, providing a positive interference in the measurement of MRP.
5 mg P/kg soil) either (a) had no effect on E-values calculated for the different soils, or, particularly for soils high in amorphous Fe, (b) led to a decrease in the calculated E-value.
However, their results could also be explained as E-values performed with [H.
p] was overestimated, and hence, E-values assessed in these soils via the standard method using 0.
It is also possible that inaccurate E-values may be obtained for soils where P is present as soluble aluminophosphate polymers or in other forms that are not molybdate-reactive, but nevertheless isotopically exchangeable (White and Taylor 1977).