Comparison of soil solution chemistry assessment using zero-tension lysimeters or centrifugation

The composition of soil solutions obtained from the field varies with the method of extraction. Variations in sampling methods and the difficulties in extracting representative samples from soils in space and time, can explain divergent results. In this study we compared soil solutions from a forest soil in northern Sweden obtained by a centrifuge drainage technique and by zero-tension monolith lysimeters. Zero-tension lysimeters were destructively sampled, and centrifuge solutions from this soil were compared with that from soil outside. In our study we found three major differences in the solute composition between the centrifugate and the lysimeter leachate: (i) larger concentrations of most solutes in the mor layer centrifugate than in the mor layer leachate, (ii) accumulation of nitrate in the lysimeters, and (iii) larger concentrations of base cations in the zero-tension lysimeters below 0.3 m depth. Water contents within the lysimeters were up to 3.5 times greater than under natural conditions and the water yields from the lysimeters indicate that water residence time ranged from <1 to >5 years. This study shows that differences in results from the two methods are due to inherent differences in the methods themselves and not just to the collection of different soil waters. The hydrological anomaly and disturbance induced by the zero-tension lysimeters affects the solute chemistry and thus the applicability of the results to field conditions.