Rescue and renewal of legacy soil inventories, a case study: semi-detailed soil surveys in some parts of Isfahan and Chaharmahal-va-Bakhtiari provinces

Soils play an important role in environmental issues and sustainable management and development programs. Then there is a growing need for the preparation of soil maps with high reliability and accuracy. Taking into account the decreasing the chance of conducting new soil surveys due to the limitation of resources, legacy soil data have been receiving a great deal of attention. These data, which carry important information about the state and properties of soil over time and place, can create a perspective for better management of different resources. Considering these issues and also the dependence of better soil management on this legacy information and the importance of using it in environmental management, serious efforts should be made to maintain and reuse these legacy soil data. Then performing some preprocesses in order to maintain and renew this information is obviously necessary, in which rescue and renewal of soil legacy inventories are the most important ones. These preprocess have to be performed before any reusing of them. In spite of global efforts in this regard, no important effort has been made to renew this valuable information so far. However, it has a good history of soil science and is full of legacy soil information inherited from pioneer soil scientists. Therefore, this study aims at rescue, renewal and evaluate available legacy soil surveys as prerequisite processes for reusing them in the framework of digital mapping.

The 10480 km2 study area is located in the border of Isfahan and Chaharmahal-va-Bakhtiari provinces. Due to the existence of Zayandehrud river in this region, it has been surveyed a lot so far. However, because of the lack of access to all these studies, three legacy soil studies covering the whole study area were selected and examined. After recording of the information of these studies in computer and georeferencing the maps, the boundaries of soil map units were digitized. The quality of the maps was afterward evaluated according to the Cornell adequacy criteria. The spatial accuracy of soil map units was then checked and their probable dislocation was finally corrected using available axillary maps and information. Also, the weighted Tau index and overall accuracy were calculated to quantitatively evaluate the quality of the maps.

The information of selected legacy soil maps and profile was successfully recorded in computer in order to keep them from destruction, and a table filled with the information of their soil profiles. The results indicate that the georeferencing of soil maps was done with relatively good quality. The results of quality and efficiency of soil map units’ assessment showed that the map scale is larger than the scale provided on the maps, however, the map legends provide enough information to the users of the map. The investigation of the boundary displacement of the map units showed that the maps had a high-level of spatial accuracy. The results of statistical evaluation of soil map units’ accuracy showed that in all studies as well as their total, the weighted overall accuracy and Tau index of the map at all levels of classification is more than 70% and 50%, respectively, which indicates a good accuracy of the maps.

Despite the public belief about the quality of legacy soil maps, the results of this study indicate well that the studied legacy soil maps have a good quality in terms of their general characteristics. It is also proved that the legacy information and maps can be used with a good degree of confidence in the digital mapping process. Thus, the cost of new soil studies can be saved using this legacy information.