SPATIAL HETEROGENEITY OF SOIL SOLUTION CHEMISTRY IN A MATURE NORWAY SPRUCE (PICEA-ABIES (L) KARST) STAND

The determination of the average soil solution concentrations in fores t soils is hindered by the spatial heterogeneity of the soil condition s and the stand structure on all scales. The aim of this paper is to i nvestigate the spatial heterogeneity of the soil solution chemistry wi thin a mature stand of Norway spruce and to evaluate the implication o f this heterogeneity for the sampling design for soil solutions. The s ite is a 140 years old Norway spruce stand of 2.5 ha located in the Ge rman Fichtelgebirge at 800 m elevation on granitic, deeply weathered b edrock. At 35 cm soil depth 59 ceramic suction lysimeters (5 nm length , 2 cm diameter) were installed in a systematic grid of 25 . 25 m and soil solution was sampled at 3 dates in June and July 1994. The soluti ons were analysed for major cations and anions. Semi-variance of the c oncentrations at a given date: revealed no systematic spatial patterns . The coefficients of variance of the element concentrations were betw een 36 and 298% with highest values for NH4+-N. The implications of th e observed heterogeneity for the appropriate number of replicates was investigated by Monte Carlo simulations. As an example, the probabilit y that the measured average concentration of SO42--S is outside a +/-1 0% range (related to the 'true' 59 lysimeter average) is about 68% if only 3 replicates could have been used, 41% with 10 replicates and 25% with 20 replicates. Due to the generally large spatial heterogeneity of the soil solution chemistry in forest soils the number of lysimeter s used must be carefully adjusted to site conditions and the specific question.