Applied digital soil mapping of agricultural land using remote sensing
Agricultural soil mapping started in the 1940s in Sweden and current recommendations suggest that one sample per hectare of arable land should be obtained. Since it is up to each farmer to invest in the soil mapping, the number of soil samples, the frequency of repeated sampling (every 5-10 years is recommended), and the analyses made in each sample, is often kept to a minimum because of short-term economic reasons. Important soil properties such as clay content and soil organic matter are often not analysed. Digital soil mapping has evolved as a discipline linking data from sensors, soil analyses and other types of data in order to produce better and more detailed maps at a lower cost.

In this project, the aim is to investigate the possibility to apply the principles of digital soil mapping in order to create very detailed maps of clay concentration and organic matter with an estimated value for each 20x20 m. The main focus will be on Skåne, the most productive agricultural region in Sweden, but also parts of the agricultural districts in Västra Götaland.

The project will be carried out during 2011 in collaboration between the Swedish University of Agricultural Sciences (SLU), Hushållningssällskapet (HS) in Malmöhus (Swedish Rural Economy and Agricultural Societies) and in Skaraborg. HS has many thousands of soil analyses (each sampling location positioned with GPS) of clay content and organic matter, but the soil samples do not cover the whole regions – they are located at mapped farms. In this project we plan to combine the available soil data with satellite images, airborne gamma ray scanning from the Swedish Geological Survey (SGU) and digital elevation data (Swedish Land Survey) to investigate if it is possible to estimate the clay and organic matter content also at farms where we not already have soil analyses.

If the project is successful it would be possible for farmers to – without having to collect and analyse a large number of soil samples – increase the precision in their crop production, by for instance more accurate use of nitrogen and lime, ultimately reducing leaching and increasing productivity.