Nearly all methods of determining P in soil involve
extraction of P into a liquid phase. Deionized w
ater (DI) is
a commonly used extractant for P analysis,
5
and ammonium oxalate (AmOx) is a multipurpose extr
actant that can be
used for cation analysis and P determination.
6,7,8
Oxalate binds to cations, pulling some of them fr
om soil particles.
An ammonium oxalate solution will extract more phos
phate from soil than will DI, because the oxalate c
an replace
the phosphate at cationic sites on soil particles.
AmOx extractions are of agronomic significance, be
cause they more
closely approximate the P that is available to plan
ts. DI extractable P is of particular environmenta
l significance,
because it is an indicator of P run-off susceptibil
ity.