Effects of Extraction Methods and Sample Storage on Properties of Solutions Obtained from Forested Spodosols

Abstract

AbstractSoil solutions obtained by three methods from Spodosols at a high‐elevation, forested study site were compared. Solutions were extracted by miscible displacement, by centrifugation, and by compressing a soil‐packed syringe. Analyses of pH, inorganic anions, total and reactive Al, and organic C showed few differences between miscible displacement and the syringe‐pressure methods. However, centrifugation at a relative centrifugal force (RCF) of 9700 m s−2 consistently produced solutions with significantly higher pH and F− content than did the other methods. Differences after centrifugation also were found in Cl−, NO−3, SO2−4, but Al, but less frequently. Effect of soil storage time on solutions obtained using the syringe‐pressure technique was studied. Both Oa and Bhs horizon samples showed large increases in solution NO−3 after 24 h of storage at 3°C. During 36 d of storage, NO−3 levels increased by as much as 10‐fold and were accompanied by pH decreases. Measurements in solutions obtained from samples that had been frozen for 36 d were higher than in the original solutions, except for NO−3 and pH. Changes with freezing appeared to be related to large increases in soluble organic C. Our results suggest that soil solution samples should be obtained very quickly after sampling of soils and that high‐speed centrifuge techniques may give erroneous results. The syringe‐pressure method is relatively rapid, simple, and easily performed in the field. However, it may not be practical under dry conditions.