Alkali, or alkaline, soils are clay soils with high pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and to be difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity. Sometimes these soils are also referred to as alkaline sodic soils. Alkaline soils are basic, but not all basic soils are alkaline.
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Alkaline soil in the context of Hortobágy National Park
Hortobágy (Hungarian pronunciation: [ˈhortobaːɟ]) is an 800 km national park in eastern Hungary, rich with folklore and cultural history. The park, a part of the Alföld (Great Plain), was designated as a national park in 1973 (the first in Hungary), and elected among the World Heritage Sites in 1999. The Hortobágy is Hungary's largest protected area, and the largest semi-natural grassland in Europe.
Until recently it was believed that this alkaline steppe was formed by the clear cutting of huge forests in the Middle Ages, followed by measures to control the course of the Tisza River, allegedly resulting in the soil's current structure and pH. However, Hortobágy is much older, with alkalinization estimated to have started ten thousand years ago, when the Tisza first found its way through the Great Hungarian Plain, cutting off many streams from their sources in the Northern Mountains. The formation was finished by grazing animals and wild horses during the Ice Age, followed by domesticated animals. The site was inscribed on the UNESCO World Heritage List in 1999 because of its long cultural history (stretching back more than four millennia), its scenery, and its testimony to traditional methods of pastoralism.