Saturday, 15 July 2006

Relationships Between Soil Properties and Environmental Biophysical Units in Milpa Alta, Central Mexico.

Jorge López Blanco Sr., Instituto de Geografía UNAM, Circuito Exterior Ciudad Universitaria, CP 04510 México, D.F., Ciudad de México, Mexico, Vela Correa Gilberto, Depto. El Hombre y su Ambiente UAM-X, Calzada del Hueso 1100 Col Villa Quietud Delegación Coyoacan, México. C.P. 04960, Ciudad de México, Mexico, and Ma. de Lourdes Rodríguez Gamiño, Instituto de Geografía UNAM,, Circuito Exterior, Cd. Universitaria, CP 04510, México DF, Ciudad de México, Mexico,, Mexico, City, AZ, Mexico.

Spatial variation of soil properties is significantly influenced by factors as climate, relief, parental material, vegetation, and anthropogenic disturbances caused by human activities. Several studies have demonstrated that soils properties are related mainly to relief characteristics in different ecosystems. Furthermore, the horizontal and vertical distribution of soils results from the influence from edaphic factors. The relationships that exist between the geomorphologic dynamic and of soil dynamic are fundamental to establish landuse potentialities within the environmental planning process. The objective of this work is to know the relationships between the physical and chemical soil properties regarding to the environmental biophysical units (EBU) applying a geomorphological approach in the delegation Milpa Alta, Central Mexico. We used 1994 aerial photographs at 1:75,000to scale to delineate the morphogenetic units that after that they were cartographic database to obtain the EBU. They were used as a base to establish the soil-sampling sites. The morphogenetic units were delineated considering the four fundamental factors of relief: General and specific origin, relief type, age-lithology and geometric class of relief. A 30-cm depth was considered to obtain the 34 soil samples distributed in the study area. Samples were dried and sieved. The physical properties considered were: moisture, porosity, bulk density, soil-color and texture. The chemicals properties were: pH, organic matter, N+, K+, Mg++, Ca++ and Cationic Exchange Capacity (CEC). The main types of relief delineated were: volcanic endogenous accumulative of mountain hillslopes of basaltic-andesitic-dacitic lava flows of Pleistocene-Holocene; volcanic endogenous accumulative of andesitic-basaltic-dacitic mountain hillslopes (cinder cones) of Pleistocene-Holocene; volcanic endogenous accumulative of high and medium hills (cinder cones) of andesitic-basaltic of Pleistocene; volcanic endogenous accumulative (andesitic-basaltic) and exogenous alluvial of local piedmont of pleistocene; exogenous accumulative Alluvial Local Piedmont of Andesitic-Basaltic Hills of Pleistocene and Exogenous Accumulative of Alluvial Plain (Crater Bottom of Cinder Cone) and Alluvial Intermountain Plain of Holocene. Results show that physical and chemicals soil properties are statistically strong related to relief characteristics. The higher moisture contain values were affected by slope inclination and its and its relief position. The topography was the main factor that explains soil variation regarding its relief situation. Slope affected the organic matter contain percentages values on sites of high both moisture contain and vegetation cover values taking as spatial reference the EBU. Most of EBUxs presented forest land cover therefore they are an important nutrients source including N, P, S, K, N, C, Mg and some micronutrients. In some cases, soil properties affect growing and distribution of vegetation types in different slope values that they are controlled by the availability of nutrients of soil. However, the differences between the EBUxs are due to the climatic conditions, the types of vegetation and mainly to the landuse of the environmental units. EBUxs soils present a high amount of organic matter and have a good aggregation. This aggregation allow a good infiltration and aeration which make to soils resistant to erosion processes and help to provide a favorable biological habitat. In the EBUxs there is a process of conversion from forest cover to agricultural land use or grassland, this reduced the organic matter amount and therefore, reduce the productivity of soil. The pH is neutral where the vegetation cover is high, mainly on mixed forest of Pinus sp, Abies sp and Alnus sp. The pH is moderately acid where the organic matter content is low and where the vegetation cover is medium with mainly Pinus sp forest. and scrub. The alluvial plain presents a pH strongly acid with a high organic matter content, due to the use of fertilizers in the agricultural activities. The soil-geomorphology relationships obtained in this work have served as a base in the decision-making process during the proposal of land management programs of the natural resources of the study area.

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