Silicophytoliths as relevant buffers in physico-chemical weathering processes in Typical Argiudolls of the Pampean Plain

OSTERRIETH, MARGARITA; BENVENUTO, MARIA LAURA; BORRELLI, NATALIA; ALVAREZ, M FERNANDA; FERNÁNDEZ HONAINE, MARIANA

Encuentro; 9th International Meeting on Phytolith Research; 2014

The agricultural productions exceed 15 million hectares in the southeast of the Pampas; 60% of these areas are predominantly occupy by wheat and maize crops and pastures, all of them important providers of silicophytoliths. The grasslands developed from the Tertiary in the Pampas, have produced silicophytoliths, biomineralizations of silt and very fine sand size, which constitute the skeletal fraction of sediments and soils. The aim of this study was to evaluate the role of the silicophytoliths in the matrix of Typical Argiudolls of the southeastern Buenos Aires. The quantitative and qualitative analysis of the silicophytolith content (status, type of alteration) in the soil horizons of the most representative Typical Argiudolls under natural conditions and with known stories of use were performed. The texture of the Argiudolls is predominantly silt sandy-clay. The silicophytoliths constitute up to 10% of the parent material (Horizons C) and up to 60% of the mollic epipedons (Horizons A), decreasing substantially toward the subsurface horizons. Studies show that the use and agricultural management of these soils generate a substantial loss of pelitic fractions. These fractions may have been reincorporated by wheat and maize crops and pastures since more than 150 years ago, through the production of silicophytoliths by these especies. Also taphonomical, mineralo-chemical and chemical studies of the soil solution show that the soil matrix is enriched in amorphous silica from the chemical degradation of silicophytoliths. Therefore, silicophytoliths originally provided by the natural grasses and later reincorporated by the main crops into the system, compensate the losses of silt and very fine sand by wind and water erosion. This work also demonstrates the importance of silicophytoliths in the preservation of the physical and chemical properties of these productive soils of the Pampas region