Effect of artificial acid rain and liming on the base status in an acid forest (Picea abies (L.), Karst.) soil (Typic haplohumod)

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Abstract
On an acid forest soil in West Jutland, Denmark, an experiment with artificially acidified rain was carried out, in order to identify the base reactions in the soil resulting from the acid rain and to localize where in the soil profile neutralization takes place. The effect of lime as an agent against the effects of artificially acidified rain was also investigated. The artificial acid rain was quantitatively neutralized in the O horizon due to ion exchange primarily with calcium and magnesium. This process produced increased concentrations of calcium, magnesium, sodium and inorganic aluminium in the soil solution sampled from E and Bh horizons. The soil did not retain sulphate, and it may be concluded that the acid is leached as metal sulphates. Also in limed plots magnesium and sodium were released from the O horizon, but to a lesser extent, and no inorganic aluminium was released into the soil solution from the E horizon. Liming may counteract harmful effects of mobilized aluminium and calcium deficiency, but must be carefully managed, because liming increases the rate of organic matter mineralization, and thus influences the very sensitive and often unstable ecosystem. Therefore, if restoration of the base status of forest soils is needed, it is recommended that slow‐reacting magnesium‐containing limestone be used at small application rates.