Saturday, 15 July 2006

The Use of the Lands and Its Adequacy in Distrito Federal, Brazil.

Fabio Alves de Carvalho and Marilusa Pinto Coelho Lacerda. Univ de Brasilia, Asa Norte, Campus Darcy Ribeiro, Brasilia, 70910-970, Brazil

The accelerated process of Distrito Federal land's occupation and the agricultural expansion are causing cerrado biodiversity's reduction, natural resources' suppression, especially soils and water. Therefore, there's a need to control and monitor the conditions of these lands in a speedy way, with the possibility of an easier periodical update of the information. That is possible through geoprocessing techniques and Remote Sensing. This work is part of a project to diagnose the Distrito Federal land's sustainability using geotecnologies to evaluate the relationships between the physical environment, emphasizing soils. It's expected that the quantitative and spatial information obtained can subsidize better regional land use planning. The researched area is named Núcleo Rural do Rio Preto, the main grains' producer of the region, measuring 376 Km². The available secondary data on natural resources and production system characteristics of the region was reviewed. To complement this information field surveys were carried out in order to verify the soil's occupation and agricultural activities and the environment. A georreferenced digital database was implemented on the ArcGIS 8.3. Thematic layers such as soils and land capability, drainage, contours and spot height informations were obtained from the topographic maps by digitizing. With the drainage, contours and spot height data it was generated a TIN (Triangular Irregular Network) of the study area. Through this TIN, it was elaborated a DTM (Digital Terrain Model). According to geomorphology and soils distribution, it was obtained 5 slope classes. An HVR/SPOT 4 image, false composition 2R3G1B, from September 2003, orbit/point 221/71, 10 meters spatial resolution was treated in ENVI 3.6. The ISODATA algorithm was used for the unsupervised classification. The thematic map Actual Land Use generated from the classified image identified the following land cover classes: Arable Areas: fields with different degrees of crop development; Bare Soils: comprehending areas prepared for cultivation and soil in degradation's process; Forest: correspondent to vegetation that surrounds water resources and cerradão (Brazilian savannah woodlands), Cerrado; Other uses: such as water resources, other types of cerrado and pastures. The maps generated were crossed using ArcGIS 8.3. The thematic layers Actual Land Use x Soils Classes, Actual Land Use x Slope Classes and Actual Land Use x Lands Capability were overlaid and the quantitative relations were evaluated. The thematic map Land's Use Adequacy resulted of the Actual Land Use and Lands Capability overlay. This layer detected areas that weren't in agreement with the established in the agricultural aptitude of the lands. The study area was divided in 2 classes: Satisfactory Use: areas that are used correctly, according to the land capability; Incompatible Use: areas that are used differently than it's recommended by the land capability. About 8% of the area is under environmental risk. The Actual Land Use map showed that the arable areas occupy 167,76 Km² (44,6%) of the total region, the bare soils occupy 116,86 Km² (31,07%), forests correspond to 26,96 Km² (7,17%), Cerrado occupies 15,91 Km² (4,2%) and Other uses are 13%. These results were confronted with the terrestrial reality, showing a good degree of reliability. The cross tabulation Actual Land Use x Soils Classes showed that 73,7% of the area are in Oxic Rhodustox dystrofic, and 34,5% of this total is in arable areas, 24% in bare soil areas. About 5,7% of the arable area is placed in Typica Haplustept, what brings concern, due to this soil type is susceptible to erosion process. The cross tabulation Actual Land Use x Land Capability showed that 85,7% of the lands are in the class of aptitude II of Land Capability Classification, and 40% of this total are in arable areas and 30% in bare soils. The cross tabulation Actual Land Use x Slope Classes showed that 29% of the arable area and 20,4% of the bare soils are in plain relief. It was observed that the water resources are pressed with the progress of the agricultural activities, like pastures and horticulture. The HVR/SPOT 4 image with the bands 1, 2, 3 was very efficient in the creation of land's occupation map. The map of Land's Use Adequacy has great importance at the evaluation of areas with degradation's risk and its stratification allows to localize the areas in critical conditions.

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