Soils of the Pampas

DIAZ ZORITA, M.; BUSCHIAZZO, D.E.

Enyclopedia of Soil Science

Marcel Dekker

Año: 2006; p. 1653 - 1657

The Pampas region is a vast plain of approximately 52 Mha located along the central part of Argentina. It is an extension of a bigger plain wedged between the Andes in the West and the GuyanaBrazilian shield in the East including the Venezuelan llanos, the Amazonian lowlands, and the Chaco-Pampas region. According to rainfall and soil quality patterns,(1) the Pampas can be divided into five subregions: Rolling Pampas, Inland or Central Pampas, Southern Pampas, Flooded Pampas, and Mesopotamian Pampas (Fig. 1). The climate is warm temperate with adequate to less than adequate rainfall for normal crop production. The mean temperature is 18°C and 14°C in the North and the South of the Pampas, respectively.(2) In part of the region, the temperature and the frost-free period are adequate for growing double crops (i.e., soybean or maize planted after wheat). Rainfall amounts show high inter-annual variability. Most rainfall occurs between October and April (spring to fall seasons), and the long-term annual average is 500 and 1000 mm in the South-West and in the North-East of the region, respectively.(2) Although, there has been an increase in precipitation in the last 20 years, at the rate of 100 mm per year,(3) the water balance during the summer is still negative with long periods of droughts of 26 weeks. Most of the region was originally covered by grasslands, interrupted only by gallery forests along the margins of the Paraná, Uruguay, and La Plata rivers. At present, most of the region is under agricultural land use and, excluding the flooded Pampas, covers approximately 34 Mha. Almost 60% of the agricultural area is covered by perennial pastures comprising alfalfa (Medicago sativa L.), fescue (Festuca arundinacea L.), and other grasses under direct grazing livestock systems. The rest of the area is involved in the annual crop production, comprising 10 Mha of soybean [Glycine max (L.) Merrill], 2.4 Mha of maize (Zea mays L.), 6.3 Mha of wheat (Triticum aestivum L.), 1.8 Mha of sunflower (Helianthus annus L.), and other crops.(4) In the rolling Pampas and in the eastern parts of the inland Pampas, almost 100% of the area falls under the annual crop sequences while the proportion of area covered by pastures increases toward the boundaries of the Pampas. The flooded Pampas is mostly under native grasslands for cattle production systems.