1.1.1. Soil acidification
According to estimates, about 9.8% of soils in the country have a pH (H2O) level <5.0 (Atanassov, 2012). Approximately 500,000 ha of acidic soils under cultivation have an acidity level that is unfavorable for some sensitive crops. The strong acidity of soils is largely associated with long-term application of unbalanced fertilization and the use of mineral fertilizers that increase soil acidity. Soil acidification is also registered as a result of SO2 emissions into the atmosphere, which enter the soil with rainwater in the form of sulfuric acid, as well as the deposition of acidic industrial waste, which is localized entirely around point sources. There are no data to assess the trend of changes in soil acidity for Bulgaria. Estimates relating to the EU (Jones et. Al., 2012) indicate a tendency to reduce acidification. This is explained by measures to reduce SO2 emissions from industrial enterprises and coal-fired power plants, and by the application of fertilization schemes that limit the use of physiologically acidic mineral fertilizers.