% aggregation and organic carbon (OC) content in soils of the Western Humid Patagonia of the Aysén Region, Chile.

Abstract

The soils (Typic Hapludands) of pastures under grazing in the intermediate-humid-temperate ecoregion of the Aysén region (humid western Patagonia, Chile) was evaluated for determination total aggregation (∑5mm–0.053mm), macro-aggregates (∑≥0.25 mm), micro-aggregates (∑<0.25 mm) and soil organic carbon (CO) content in the aggregated structures. Established conditions were: terrace in degraded natural pasture (TPD), terrace in well-kept planted pasture (TPBE), silvopasture (SP), degraded natural pasture on a hill site (LPD), and well-kept planted pasture on a hill site (LPBE) at depths of 0-5, 5-10 and 10-20 cm. All the conditions studied have high total aggregation. SP has a high content of macro-aggregates; in the opposite way, TPD has a higher percentage of micro-aggregates.  The CO between treatments was variable. SP macro-aggregates presented the highest percent CO (8.6±1.74), followed by hill site (LPD, LPBE) and terrace (TPD and TPBE) treatments. The highest percent CO in micro-aggregates was on the hill site (LPD 9.55±1.84 and LPBE 8.13±2.11), followed by terrace treatments (TPBE, TPD) and the lowest was SP (6.78±1.49). In depth (0-20 cm) percent CO in macroaggregates and micro-aggregates decreased significantly 37percent and 41percent respectively.  It is concluded that SP presents ecological conditions that promote aggregation with a higher content of maco-aggregates; In addition to providing percent CO congregated in the macro-aggregates. A relationship between degraded systems (degraded grasslands), a higher percent of micro-aggregates and a higher percent CO in micro-aggregates is inferred, which coincides with that proposed by several authors in that the micro-aggregate has greater physical structural stability and is important CO reservoir.