S. Kuo et Ej. Jellum, THE EFFECT OF SOIL-PHOSPHORUS BUFFERING CAPACITY ON PHOSPHORUS EXTRACTION BY IRON OXIDE-COATED PAPER STRIPS IN SOME ACID SOILS, Soil science, 158(2), 1994, pp. 124-131
Iron oxide-coated strips can serve as a P sink to continuously remove
P from solution. In this way, P extraction is analogous to P absorptio
n by plant roots. Because the relationship between soil P sorption cap
acity and P extraction by the Fe oxide-coated strips can affect the in
terpretation of the P test values, it needs to be examined. The effect
iveness of the Fe oxide-coated strips in extracting sorbed P, and its
relationship with soil P sorption capacity and with the commonly used
NaHCO3 P test, were evaluated in acidic soils amended with varying amo
unts of P. Both the Fe oxide strip and NaHCO3 P tests were correlated
with corn (Zea mays L.) dry matter yields to determine their relative
effectiveness in describing plant growth response to increased P avail
ability in soils. Iron oxide strip-extractable P, like NaHCO3-extracta
ble P, increased with increasing amounts of P added to the soils. The
recoveries of sorbed P by the two test were similarly affected by the
P sorption capacities of the soils at a solution P concentration of 9.
7 x 10(-6) M or at a constant P addition of 20 mmol kg-1, which explai
ns the close correlation between the two tests (R2 = 0.85, P < 0.001).
The Fe oxide strip-extractable P reflected more appropriately an inte
nsity index, rather than a quantity index, in the characterization of
soil P availability. Decreased P extraction by the Fe oxide strips at
high ionic strengths indicated that desorption of sorbed P from soil l
imited P extraction by the Fe oxide strips and that maintaining simila
r ionic strength is important in assessing P availability among divers
e soils. Both the Fe oxide strip- and NaHCO3-P tests correlated well w
ith corn yields, tissue P concentration, and P uptake. The Fe oxide st
rip P test did not seem to have much advantage over the NaHCO3-P test
in describing corn response to increased P availability in the soils;
however, the Fe oxide strips can be stored easily for later analysis o
r sent to centralized locations for P determination, if necessary.