Soils of Pampa Gaúcho, the Mixed Prairies of Southern Brazil

Abstract

The Mixed PrairiesPrairies soils region of southern Brazil, popularly known as “Pampa Gaúcho”, constitutes one of the most important and exceptional landscapes in the country, dominated by gentle undulating relief with hilly slopes, known as “coxilhas”. Grasslands are dominant in the pampas, representing a relict of drier past climate, and constrained by the anthropic pressures, burning, and clearing for expanding cattle or agriculture. The past drier phase left a legacy of high fertility soils, expansible 2:1 clays, calcium carbonate concretions, and polychromy. However, dystrophic soils of low natural fertility also occur, notably on quartz-rich sandstones, also prone to severe water and wind erosion under the current climate, and unfavorable to agriculture use, forming widespread arenization. Although livestock is the dominant activity in the pampas, irrigated rice cultivation also has a marked geographic and economic importance in wetlandTropical wetlands areas. Increasing grain production in the recent decades mainly occurred with the incorporation of sandy, fragile areas into the production process. The use of shallows soils, such as Neossolos Litólicos (Lithic Leptosols) and Neossolos Regolíticos (Regosols) by rice cultivation in a flooding system raises concerns about the sustainability of this intensive use, despites the natural high fertility of the soils. Regarding the Vertissolos (Vertisols) and Chernossolos (Chernosols), clayey or very clayey textures and the predominance of expansible 2:1 clays makes these soils extremely fragile when intensive agricultural use is adopted, besides the natural vulnerability to compaction and water erosion, due to high dispersibility of the clay fraction and poor drainage. Erosion features, such as rills and gullies are commonly found. A rich and diverse Grassland is typical of the pampas, and this rich flora sustains the traditional livestock in the Campanha but has been gradually modified by anthropic action, with burning cultivated pastures Pine and Eucalyptus reforestation and agriculture. The “southern Grassy fields”, Pampas, constitute a neglected biome, with only a minor part duly protected by Conservation Units (UC), equivalent to less than 0.5% of the total area. The Domain of Mixed PrairiesPrairies soils (pampas) in Southern Brazil is the only true temperate/subtropical landscapeSubtropical landscapes in the country, with high aesthetic value, beauty of ecological and cultural importance. Its unique soils result from past and present climates, shaping a polycyclic landscape with a singular and dominant grassland vegetation. The long-term sustainability of the Pampas in Brazil is challenged by a combination of widespread eolian and water erosion, rapid expansion of forestry monoculture, technological advance of cash-crops, and urbanization.