Current Agriculture Expansions and the Risk of Dryland Salinization in Central Argentina

JAYAWICKREME, D; SANTONI, C; NOSETTO, M D; KIM, J H; BALLESTEROS, S I; JOBBÁGY, E G; JACKSON, R B

Congreso; American Geophysical Union. Fall Meeting; 2010

The increasing global demand for agricultural commodities is rapidly transforming land cover in South America. In central Argentina, vast tracts of natural woodland and grassland ecosystems are converted each year primarily for a larger share of the world’s soybean market. Invisible to land-owners, policy makers and many others alike, these land-cover conversions are altering the water balance over the landscape. Our research finds that in semi-arid areas of central Argentina, the introduction of rain-fed agriculture increases deep drainage and groundwater recharge from 1 mm/yr in natural woodlands to over 15-30 mm/yr in agriculture, leaching large amounts of salts accumulated in the vadose zone during the last ~10000 years. Our estimates along the western edge of Pampas suggest that each hectare of woodland that is converted to agriculture can potentially release over 100 tons of salts from the vadose zone to the groundwater. Evidence from an agriculture chronosequence (6-90 years) further showed that salt leaching from the vadose zone is rapid in the sandy aeolian sediment formation that extend from the Andes to the Atlantic ocean across central Argentina. While the regional hydrological links between the semi-arid highlands and the highly productive Pampas lowlands, only ~150km to the east are still not well established, geological and geomorphological traits suggest that the current wave of agriculture expansion in the semi-arid highlands has the potential to raise groundwater levels and salinity and affect long-term agriculture productivity regionally.