Estabilidad estructural del suelo bajo diferentes sistemas y tiempo de uso en laderas andinas de Nariño, Colombia

To evaluate the impact of different land use systems for long periods of time on soil structural properties, a sampling to 0-20 cm of depth was carried in the following treatments: Forest 25% slope (control), pasture crops for 25 years with 25% slope and use agricultural wheat-corn (rw-c) of 25, 45 and 70 years of use, each one of these last, with 12% and 25% slope, in a Inceptisol (Dystric haplustepts) of the area of reconversion of the wheat cropping area located at 2.400 to 2.800 masl in the Andean zone of the department of Narino, Colombia (longitude 75° 14' west, latitude 0.5° 10' north, 2710 msnm, 80% RH, 12°C). Results showed significant differences between the type and intensity of soil use for long periods of time in aggregate size distribution, aggregate stability and pore size distribution. The increment of the intensity of soil use, decreased its structural stability and affected soil porosity. The percentage of water stable aggregates larger than 2.0 mm was significantly higher in not intervened soil. The control had 51.5% of water stable aggregates larger than 2.0 mm. Change to agricultural use (rw-c) during 25,45 and 70 years, decreased the stable aggregates larger than 2.0 mm, to 36.9%, 35.3%y 29.1% respectively. The change of forest to pasture, decreased the total porosity in 18%. The agricultural use (rw-c) through the time, generated gradual decrease of the total porosity.