This study used archived remote sensing images to depict the history of changes in soil salinity in the Hetao Irrigation District in Inner Mongolia, China, with the purpose of linking these changes with land and water management practices and to draw lessons for salinity control. Most data came from LANDSAT satellite images taken in 1973, 1977, 1988, 1991, 1996, 2001, and 2006. In these years salt-affected areas were detected using a normal supervised classification method. Corresponding cropped areas were detected from NVDI (Normalized Difference Vegetation Index) values using an unsupervised method. Field samples and agricultural statistics were used to estimate the accuracy of the classification. Historical data concerning irrigation/drainage and the groundwater table were used to analyze the relation between changes in soil salinity and land and water management practices. Results showed that: (1) the overall accuracy of remote sensing in detecting soil salinity was 90.2%, and in detecting cropped area, 98%; (2) the installation/innovation of the drainage system did help to control salinity; and (3) a low ratio of cropped land helped control salinity in the Hetao Irrigation District. These findings suggest that remote sensing is a useful tool to detect soil salinity and has potential in evaluating and improving land and water management practices.
In the irrigated scheme of West Mitidja, access to land and water is ensured through countless local informal arrangements. The assignees of small collective farms have subdivided the land informally, and rent out part of it to lessees, thereby circumventing current legislation. The surface irrigation system provides only a small proportion of irrigation water to farmers, who rely mainly on groundwater for irrigation. The results of our analyses show that the agricultural dynamics of this perimeter are to a large extent ensured by ''invisible'' farmers cultivating land obtained through informal land markets and using groundwater via ''illicit'' tubewells. These farmers are also important vectors for innovation (new irrigated cropping systems, drip irrigation). We organized a series of workshops with farmers (assignees and lessees) and government agencies to explore agricultural development and water management perspectives in the area. Our work showed that it is land and water markets that should be formalized rather than land or water property so that lessees will be considered as actors for water management and agricultural development in the area.
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