Monday, 10 July 2006

Salt Dynamic in “Patched” Soil of Crops in Argentina.

Eugenio Hampp, Elena Bonadeo, Marcos Bongiovanni, Inés Moreno, and Rosana Marzari. Universidad Nacional de Río Cuarto, Ruta 36 - Km 601., Río Cuarto - Córdoba, Argentina

Patching (P) of crops is a phenomena characteristic of the “Pampa Plana” in the Province of Córdoba, Argentina. This area is a geomorphologic unity with subnormal relief. Patches are areas where plants show less growth than those considered Normal (N). Their dimensions are in a range of a few square meters and their boundaries are abrupt. It has been found out that soils with patches contain soluble salts at different depth. There is a relationship between patching and soils where salts are at 15-20 cm deep with an Electrical Conductivity (EC) that increases rapidly from 0.4-0.5 dSm-1 in the surface to about 7.5 dS.m-1 at about 50 cm depth. In the “N” areas ECe range between 0.4-0.5 dS.m-1 from the surface to 50 cm depth, reaching values of 3.0 dS.m-1 at 70-80 cm. depth. The objective was to characterize “P” and “N” and to interpret their current salt dynamics. In a representative area, the studied soils are typic Haplustolls that show a quick change in salinity and alkalinity with depth while salt never reaches the surface. The “Pampa Plana” region has a subhumid-dry climate with a monzonic regime. The studied area is located at 32º 28'S and 62º 18'W. Using a regular systematic sampling in an area of 8 ha, high and low spots were chosen according to their salinity. EC(1:1) was measured at the depth of 50 cm in the samples. Soil profile morphological properties were described in “N” and “P”. Infiltration (I), bulk density (BD), cationic exchangeable capacity (CEC), exchangeable Ca++; Mg++; K+ and Na+ , pH and particle size distribution were measured. Results shows that in the “P” areas BD is higher and I values are lower, being both parameters related to slow HC. A rather opposite situation was found in the “N” areas. As water rain infiltrates soluble salts dilute and an intense dispersion of the colloidal complex takes place due to the salt types (approximately 90% sodics), their high concentration and RAS values. Higher ESP and pH values confirm the results. This dispersion process results in less permeability and leaching, creating a soil condition that stays unchanged in time. In “N” areas salts are better leached and reach deeper levels owed to the more favorable conditions for soil floculation. Key words: Hapludolls, Salinity, Alcalinity, Floculation, Dispersion, Permeability.

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