Js. Bhatti et al., INFLUENCE OF SOIL ORGANIC-MATTER REMOVAL AND PH ON OXALATE SORPTION ONTO A SPODIC HORIZON, Soil Science Society of America journal, 62(1), 1998, pp. 152-158
Oxalate is one of the dominant low molecular weight organic anions in
many soils under forest ecosystems. Through its complexation reactions
with Fe and Al, both in solution and at mineral surfaces, oxalate inc
reases the availability of nutrients such as P in these soils. This in
vestigation was designed to study (i) the influence of pH on the mecha
nism of oxalate sorption by the soil clay fraction and whole soil mate
rials from a spodic horizon, and (ii) the effect of soil organic matte
r removal on oxalate sorption using Fourier-transform infrared (FTIR)
spectroscopy. The removal of soil organic matter and decrease in pH in
creased oxalate sorption significantly, There was a two- to threefold
increase in oxalate sorption with removal of organic C at all pH value
s, Depending on pH, the molar ratio of OH ions released to oxalate sor
bed,vas close to 1 or 2, These results suggest that oxalate formed mon
dentate and/or binuclear surface complexes at pH 3.5, and bidentate su
rface complexes at pH 4.5 and 5.5. With oxalate sorption, large amount
s of organic C and Al were released from the soil clay fractions and w
hole-soil samples. Seven to 10 times more organic C was desorbed by lo
ading of 10 mol oxalate kg(-1) soil clay than by water.