SOIL DRYING AND REWETTING, OR FREEZING AND THAWING, AFFECTS SOIL SOLUTION COMPOSITION

Analysis of soil solution is a useful tool for soil fertility characterization and environmental studies, yet little is known about the effects of soil storage and handling on the solution collected. A laboratory study was conducted to determine the effects of time of extraction and preextraction freezing and thawing, or drying, rewetting, and incubating on centrifugally collected soil solutions. The relationship between electrical conductivity (EC) and ionic strength (I) also was studied. Samples of Bt horizons of three Hapludults were centrifuged at 750 g and solutions were collected after 20, 60, 120, and 240 min. Solutions were collected from fresh soils and from soils that had been frozen and thawed, or air dried and rewetted to their original water content, and then incubated for various periods of time. Solutions were analyzed for EC, pH, NH4, Ca, K, Mg, Na, Cl, F, NO3, and SO4. Significant changes in soil solution composition were found as centrifugation time was varied, indicating the importance of this parameter in soil solution extractions. The relationship between EC and I was very close to those previously described; EC can provide a good estimate of I of soil solutions. Soil solution composition was substantially altered by preextraction drying-rewetting or freezing-thawing. Following incubation, the composition of soil solutions from rewetted soils did not approach that of fresh soils. Neither of the methods studied here provided a good means of storing soil samples prior to soil solution extraction.