Abstract

Unsustainable management of the "Espinal" agroecosystem of central Chile has progressively lowered the organic matter content and fertility of soil as evidenced by decreasing forage production and lower coverage of espino (Acacia caven (Mol.) Mol.), a leguminous tree. This savannah-type ecosystem includes the soil Cauquenes clay loam (Ultic Palexeralfs; Umbric Acrisols) that formed in granitic residuum, and a Mediterranean-type climate having extended dry periods during the warmer months (November through March). Considering that productivity is related to soil organic matter, the objectives of this investigation were to determine the content of organic carbon (C) in soil of well preserved, typical and degraded Espinals; evaluate fractions of the soil organic matter as indicators of sustainable management; and use the Century model to determine the potential gains of C in the soils. Well-preserved, typical, and degraded Espinal sites were located near Cauquenes, Chile, and soil samples were collected in three representative subsites at 0-20 cm and 20-40 cm depths. In the laboratory, organic matter was fractionated using distilled water to isolate the light fraction, and C content was measured using dry combustion of the separate fractions. Century was calibrated to local conditions and simulations were run using current and less intensive management. The results indicated that total soil C of typical and degraded Espinals was 18 and 49% lower, respectively, than in soil of the well-preserved Espinal, and that the ratio of C in the light fraction between the two soil depths may be a useful indicator of sustainable management. Model simulations forecasted that soil C would slowly increase in the degraded Espinal by 3.19-3.86 Mg ha-1, after 100 years. Copyright © Taylor & Francis Group, LLC.