Data from: Soil solution in Swiss forest stands: a 20 year's time series

Soil solution chemistry is influenced by atmospheric deposition of air pollutants, exchange processes with the soil matrix and soil-rhizosphere-plant interactions. In this study we present the results of the long-term Intercantonal Forest Observation Program in Switzerland with soil solution measurements since 1998 on a current total of 47 plots. The forest sites comprise two major forest types of Switzerland including a wide range of ecological gradients such as different nitrogen (N) deposition and soil conditions. The long-term data set of 20 years of soil solution measurements revealed an ongoing, but site-specific soil acidification. In strongly acidified soils (soil pH below 4.2), acidification indicators changed only slowly over the measured period, possibly due to high buffering capacity of the aluminum buffer (pH 4.2 – 3.8). In contrast, in less acidified sites we observed an increasing acidification rate over time, reflected, for example, by the continuous decrease in the ratio of base cations to aluminum (BC/Al ratio). Nowadays, the main driver of soil acidification is the high rate of N deposition, causing cation losses and hampering sustainable nutrient balances for tree nutrition. Mean nitrate leaching rates for the years 2005-2017 were 9.4 kg N ha‑1 yr‑1, ranging from 0.04 to 53 kg N ha‑1 yr‑1. Three plots with high N input had a remarkable low nitrate leaching. Both N deposition and nitrate leaching have decreased since 2000. However, the latter trend may be partly explained due to increased drought in recent years. Nonetheless, those high N depositions are still affecting the majority of the forest sites. Taken together, this study gives evidence of anthropogenic soil acidification in Swiss forest stands. The underlying long-term measurements of soil solution provides important information on nutrient leaching losses and the impact climate change effects such as droughts.. Furthermore, this study improves the understanding of forest management and tree mortality regarding varying nitrate leaching rates.Please consider the corresponding ReadMe file of the data sets. All R-codes of the data manipulation and analysis of the various models are given in the RMarkdown file in the R-Project folder. Funding provided by: Bundesamt für UmweltCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100003338Award Number: Funding provided by: Swiss cantons AG, BE, BL, BS, FR, SO, TG, ZH and the environmental offices of the cantons in Central Switzerland.*Crossref Funder Registry ID: Award Number:Please check material and methods section of the full paper published in PLOS ONE