assessment of changes in the phosphorus status of forest ...

enhances the dissolution of Ca-phosphates. Moreover, this extracting solution
removes dissolved and adsorbed P on calcium carbonate and other surfaces (Al- and
Fe-oxide). As expected, this method would extract a significant amount of organic
matter and thus P associated with it. In recent years, this method has been included in
the sequential extraction procedure, where both the inorganic P and organic P forms
extracted by this method are described as readily labile forms. There is very little
evidence to show that the organic P fraction extracted by this reagent is readily
mineralisable and can be treated in the same category as the inorganic P fraction. This
method has been used to detect short-term changes in the amount of P in forest soils.
For example, Bekunda et al. (1990) showed that changes in the amount of inorganic P
owing to different forms of slash management at the time of plantation establishment
could be measured by the NaHCO3 method with good results, though not for organic
P measured in the extract.
Solutions containing lactate and citrate anions are also extensively used to release P in
soil test methods. These methods are based on the desorption and exchange of P from
various soil components. In Germany, Scandinavia and many East European
countries different versions of the lactate method which was suggested by Riehm
(1947) are used. Of the two commonly used versions, CAL (calcium lactate and
acetic acid at pH 3.5) dissolves less P than the DL (Double lactate) method. The
method extracts comparatively low values of P from forest soils, when compared to
soils from agricultural land uses, as can be been in the Fig 13 taken from Leinweber
et al. ( 1993). Thus the usefulness of the method to detect small changes in P status of
forests soils is highly questionable. This method may however be useful for assessing
short term changes in forest soils, eg., after fertilizer additions.
Mehlich used a combination of HCl and H2SO4 acids (Mehlich 1) to extract P from
soils in the north-central region of the U.S. which he modified (Mehlich 1984) to
develop a multi-element extractant. Mehlich 3 extractant is a combination of acids
(acetic and nitric), salts (ammonium fluoride and ammonium nitrate), and the
chelating agent (EDTA). This is a commonly used method, also for forest soils in
parts of USA. These methods as the other methods mentioned above provide useful
results for specific short term changes in P status, but as shown by Richter et al.
(2006) this method could not predict the long-term amount of P taken up by an
aggrading pine ecosystem.
Use of anion exchange resin acting as a sink to extract P has been in use for a long
time. In recent years an impregnated paper with anion exchange resin (Sharpley 2000)
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