RESPONSE OF SOIL-WATER CHEMISTRY TO EXPERIMENTAL CLEAN RAIN IN THE NITREX ROOF EXPERIMENT AT SELLING, GERMANY

In the Selling experimental forest in central Germany a manipulation s tudy with three roof constructions of 300 m(2) area each is underway i n a 60-year-old Norway spruce (Picea abies (L.) Karst.) forest. The ex perimental treatments are: (1) 'clean rain' roof with simulated pre-in dustrial throughfall; (2) control roof for roof effects alone, without manipulation; (3) drought/rewetting roof, for simulation of extreme d rought; (4) control without roof. The clean rain roof is part of the N ITREX project; we investigate the time scales and biological reactions of the system which lead to reversal of nitrogen saturation. The data include soil water chemistry for 2 years prior to treatment and 1.5 y ears of treatment. The response to reduced inputs of N and S was lower concentrations in soil solution of N ions, sulfate and Al down to 40 cm depth. Nitrogen ions virtually disappeared from the soil water in t he rooting zone (less than 70 cm soil depth) during the 1.5 years of c lean rain application. If this trend continues, nitrogen leaching will cease within a relatively short period of time, and N-saturation will be reversed. Future studies will focus on the reaction of the forest to the significantly reduced N levels in soil solution.