ChileanJAR

Retention and enhancement of soil organic carbon content is important in maintaining soil fertility and structure. The objective ofthis research was to determinate organic carbon distribution in two agroecosystems with yerba mate cultivation. The concentration oftotal soíl organic carbon (CO) in aggregate size fractions separated by dry and wet sieving of several treatments of a cultivated and virgin Kandihumult from the Misiones Province, Argentina (27°39' South Lat., 55°26' West Long.) was studied. The agroecosystems assessed were: a) Native forest subtropical soil; b) A 50 year-old "yerba mate" crop (Ilex paraguariensis Saint Hil.) with mechanical weed control between crop lines; c) The same as b) but with no mechanical weed control between crop lines; and d) A 50 year-old "yerba mate" crop with elephant grass (Pennisetum purpureum Schumach) between the crop lines which was used as green manure during the last six years. A large proportion of the total soil dry weight was isolated in the macroaggregate (>250 μm) size class in aH treatments with dry and wet sieving. It was found that native forest soil was more stable than cultivated soíls, whereas the soil covered with elephant grass was more stable than the yerba mate soil with mechanical weed control. The highest concentration of CO was found in: (1) the native virgin forest soíl, (2) the upper (0-5 cm) soillayer, and (3) the microaggregate <250 μm) soil fractions. Elephant grass treatment appears to be a useful management practice to retain and increase soil organic carbono