Saturday, 15 July 2006

Long-Term Salinization Dynamics of Irrigated Soils in the Golodnaya Steppe (Uzbekistan) as Determined from the Remote Sensing Data.

Ekaterina V. Vilchevskaya and Natalya V. Kalinina. V.V. Dokuchaev Soil Science Institute, Pyzhevskii per. 7, Moscow, Russia

Soil properties are subjected to temporal changes making it necessary to study their dynamics. Soil salinity is one of the most dynamic soil characteristics. It is known that some soils can change their status from nonsaline soils to strongly saline soils within a year. The temporal dynamics of soil salts are especially significant for irrigated territories. The development of computers and corresponding algorithms and the availability of remote sensing data have contributed to a significant progress in the monitoring of soil salinity. The creation of the geographic information system and the use of partly automated procedures for interpreting remote sensing data (satellite and aerial imagery) have made it possible to trace the dynamics of soil salinization within the Usman Yusupov farm in the Golodnaya Steppe of Uzbekistan. At the first stage, we used panchromatic aerial photos made in the period between irrigations (August–the beginning of September) and before defoliation; these photos were available for a period from 1982 to 1990. Their interpretation (in terms of soil salinity characterization) was based on the methodology suggested by Pankova and Mazikov in 1985. For the period after 1990, it was impossible to obtain the corresponding aerial photos; the images made from LANDSAT 5-7 satellites were used. As we failed to obtain panchromatic images satisfying the requirements for adequate interpretation, synthesized images from channels 7, 4, and 2 were used. This procedure was based on the methodology elaborated earlier for multispectral aerial photos. As a result of the interpretation of the aerial photos and LANDSAT imagery, seven maps characterizing the dynamics of soil salinization within the farm from 1982 to 2002 were compiled. The maps show the areas with different salinization degrees grouped into four categories: nonsaline and slightly saline soils, moderately saline soils, strongly saline soils, and extremely strongly saline soils (solonchaks). The areas shown on the maps for different years were compared, which made it possible to trace the dynamics of soil salinization. The following patterns of soil salinization processes were distinguished: (1) areas with stable salt status, (2) areas subjected to progressive salinization, (3) areas subjected to progressive desalinization, and (4) areas with differently directed salinization–desalinization processes without definite trend. If the maps for two or three years are compared, soils with different patterns of salinization dynamics occupy approximately equal areas; the changes in salinity of particular soils are from one to three grades (i.e., from nonsoline to strongly saline, etc.). However, if we compare the maps for the entire period of soil salinity monitoring, the situation will be different. In this case, areas of soils with stable salt status occupy only 1–5% of the farmland; areas with progressing desalinization, 10–15%; areas with progressing salinization, 10–15% as well; areas with variable soil salinization degree without any definite trend of changes predominate and constitute about 70–80% of the farmland. In about 50% of the areas with progressive soil salinization this process is conditioned by the natural factors. The progressing soil salinization in the remaining 50% of such areas (including the areas with strongly saline soils) is due to the anthropogenic impacts. In general, it can be concluded that soil salinization dynamics within the studied territory have no definite trends; salinization–desalinization processes alternate in most of the soil areas studied, which may be related to different character of anthropogenic impacts on the territory.

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