Soil solution

The soil solution occurs as the center-piece of the soil nutrient pool diagram with all nutrient pools, biosphere reactions, atmospheric inputs, and leaching connecting through the soil solution. Thus, the soil solution pool is very dynamic and sensitively responds to changes in any part of the nutrient supply/demand system. Soluble nutrients are readily available for plant uptake and it is believed that most elements must be released to the soil solution before they are available for biological uptake. The pool of nutrients contained within the soil solution at any one time is very small; however, the flux of nutrients through the soil solution pool may be very large. This is well illustrated by the N cycle in which the soil solution concentrations may be low to non-detectable in N deficient ecosystems. In contrast, the flux of N through the soil solution is often on the order of 30-90 kg/ha/yr because N released by mineralization is immediately taken up by biota and thus remains in the soil solution pool for only a short period of time. Due to the sensitive and dynamic response of soil solutions to ecosystem processes, collection and analysis of soil solutions is a powerful approach for examining nutrient dynamics at the ecosystem scale. In situ soil solutions can be sampled by centrifuging solutions from solid-phase samples or by use of tension or zero-tension lysimeters to extract water from soils in the field.