| Sumario: | Soils located in different altitudinal belts between Tumaco (Pacific Ocean) and Galeras Volcano (4250 m above sea level) Nariño, SW Colombia, were studied to determine the variation of some chemical properties as affected by the altitude. Between 1000 and 4000 m organic matter and total-N increased with the altitude. For pH, Ca, Mg, Na, K and P there was no good relationship wth altitude following trends were noted: pH, exchangeable Ca, Mg and Na as well as per cent clay decreased slighly with an increase in altitude. Exchangeable K appeared to increase and the concentration of P was irregular with an increase in altitude. In all areas CEC was organic matter dependent, It appears that in this region volcanic materials form the Andean Highlands (Galeras, Azufral, Cumbal, etc. volcanos) thoroughly disseminated by winds, running streams and by leaching, have been a major influence in the soil chemical properties
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