Drought experiments within the Solling roof project

Abstract Results of drought/rewetting experiments are presented, they were designed as patch-scale field experiments in a strongly acidified Norway Spruce plantation at Solling, Germany. The major objective of the experiments was to investigate if summer droughts and subsequent rewettings can lead to mineralisation/nitrification pulses. These pulses may acidify the soil solution due to the formation of nitric acid. Artificial droughts were produced by using a permanent roof construction installed below the forest canopy. Artificial rewetting was carried out with collected and stored throughfall water. Three drought periods were induced between 1992 and 1994. The soil solution chemistry indicated no distinct nitrification pulses after any of the droughts. Only single samples showed slightly elevated nitrate concentrations and decreased pH values. During the first days of the rewetting phases peaks of NH 4 + , K + and DOC were detected in the soil solution of the upper mineral soil, but also in the seepage output (100 cm soil depth). Flux calculations indicate an elevated output of K + during rewetting but also a net accumulation of nitrate for the drought plot.