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

is commonly saturated with HCO3 is mostly used, but OH saturated resin is also used.
Resin beads are packed in bags (Brewster et al. 1975, Sibbesen 1978, Bache and
Ireland 1980) for such studies or more recently, anion exchange resin papers have
been successfully used to desorb P from soils (Saggar et al. 1990, Schoenau and
Huang 1991, Nuernberg et al. 1998, Sato and Commerford 2006). It appears that there
is no experience on the use of anion resin papers to desorb P from organic rich forest
soils of Germany.
A repeated extraction method has been suggested by others (Delgado and Torrent
1997, Bhatti and Comerford 2002, ), but this has not been used for desorption of
native P. Such a method will also provide parameters which can be used later for
models involving kinetics of P desorption (Koopmans et al. 2004). A set of selected
soils from BZE2 should be included for preliminary experiments and for obtaining
desorption isotherms.
• Further development of methods to assess desorption parameters for BZE2
samples
The suggested method is resource intensive and not suitable for wide range of survey
work. There are two possible alternatives which would require further experimental
development:
(a) use of pedo-transfer functions to find relationships between easy to measure soil
parameters and desorption parameters obtained from the sequential extraction
procedures. A number of attempts have been made recently to find out if the
adsorption and desorption parameters can be estimated by means of pedo-transfer
functions (Borggaard et al 2004, Barros et al 2005). Barros et al (2005) considered
the possibility of using pedo-transfer functions to assess the desorption and
adsorption parameters of Cerrado soils. They considered clay content and the
amount of labile P on soil surfaces to relate to Kd values of resorption and
desorption isotherms. Phosphorus desorption was measured using anion-exchange
membranes. Sorption was a function of soil clay content, and a pedo-transfer
function for the soil partition coefficient was calculated with an r 2 =0.99.
Desorption and resorption were dependent on both the clay content of the soil
(r 2 =0.59-0.99) and the amount of sorbed labile P.
This procedure may not be useful unless soil parameters required for estimating pedotransfer
functions are available for each site, which in BZE 2 may not be the case. But
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