Harmonizing legacy soil data for digital soil mapping in Indonesia

Abstract Soil legacy data are basic input data for digital soil mapping. Any monitoring of global soil change cannot be successful unless soil data availability and characterization at the national level are well understood. Spatial data infrastructure frequently hampers many developing countries to take advantage of their soil legacy data for digital soil mapping at the national and regional level. While the initial purpose for developing a soil database is to store survey data, it cannot be efficiently used to support quantitative, digital soil mapping and assessment. This paper aims to develop a prototype soil observation database for global soil mapping in Indonesia. We will outline the steps needed to prepare legacy data for digital soil mapping, and describe the challenges and the Indonesian responses. The steps cover (i) legacy data identification and collection, (ii) data selection, (iii) database development and population, (iv) data harmonization and display, and (v) dataset integration. Because of uncoordinated and poorly-defined soil databases, we have to resort to a pragmatic approach to build a new and simpler database to support mapping activities. Historical soil survey reports and soil maps were collected, scanned, and summarized. After various considerations, we decided to only use soil profile observations which have clear geographical coordinates. We designed a database for soil profile observations and implemented it at two levels: spatial site data and horizon data. Spatial site data includes site geographical coordinates and attributes, while horizon data includes soil physical and chemical properties. The depths of soil profile database entries were standardized using the equal-area spline. Soil legacy data management for supporting digital soil mapping and GlobalSoilMap.net project are then discussed. These steps and data management are found helpful in Indonesia and this experience may be useful for other countries having similar impediment.