Collection of soil solution

The collection and analysis of the in situ soil solution is important for studies of pedological processes, environmental quality monitoring, and nutrient cycling (Zabowski and Ugolini 1990). Soil solution measurements are relevant for plant uptake and nutrient availability concerns, and estimates of solution fluxes from ecosystems are needed to balance ecosystem nutrient budgets and for research questions addressing losses of elements via leaching. Although laboratory soil extracts using chemical extractants or resin bags may measure an index of time-integrated nutrient availability, such extracts cannot measure fluxes within or between ecosystems.
Soil solution can be measured either by collecting field-moist soils and extracting solutions in the laboratory or by collecting solution in the field, usually with lysimeters. We will discuss three soil solution collection and measurement techniques here: field exchange resin membranes, soil lysimeters, and laboratory extraction of soil solution. Each technique measures something slightly different, and the technique needs to match the specific research question. Zero-tension lysimeters may be most appropriate for measuring fluxes through the soil profile and absolute losses from the system, while tension lysimeters can measure soil solution chemistry by depth and are indicated for questions relating to solution-solid phase equilibria or plant nutrition (Lajtha et al. 1995; Marques et al. 1996). Field resin measurements reflect both diffusion coefficients and mobile soil concentrations, and are often used to measure in situ nutrient availability. Laboratory extraction of soil water is generally less invasive and time-consuming than lysimeter installation and maintenance, and is useful for measurements of the intensity of soil solution. Detailed discussion of methods, as well as comparisons among methods, is offered in each section.