Mohamed Badraoui

Soil legacy data rescue via GlobalSoilMap and other international and national initiatives

Legacy soil data have been produced over 70 years in nearly all countries of the world. Unfortunately, data, information and knowledge are still currently fragmented and at risk of getting lost if they remain in a paper format. To process this legacy data into consistent, spatially explicit and continuous global soil information, data are being rescued and compiled into databases. Thousands of soil survey reports and maps have been scanned and made available online. The soil profile data reported by these data sources have been captured and compiled into databases. The total number of soil profiles rescued in the selected countries is about 800,000. Currently, data for 117, 000 profiles are compiled and harmonized according to GlobalSoilMap specifications in a world level database (WoSIS). The results presented at the country level are likely to be an underestimate. The majority of soil data is still not rescued and this effort should be pursued. The data have been used to produce soil property maps. We discuss the pro and cons of top-down and bottom-up approaches to produce such maps and we stress their complementarity. We give examples of success stories. The first global soil property maps using rescued data were produced by a top-down approach and were released at a limited resolution of 1km in 2014, followed by an update at a resolution of 250m in 2017. By the end of 2020, we aim to deliver the first worldwide product that fully meets the GlobalSoilMap specifications.

Mapping the Risk of Soil Salinization Using Electromagnetic Induction and Non-parametric Geostatistics

The knowledge about the magnitude, the spatial extent, the distribution and the evolution of salinity over a period of time is essential for the better management of salt-affected soils. Soil salinity is determined, conventionally, by measuring the electrical conductivity of a saturated past extract (ECe). However, given the spatio-temporal variability of salinity, numerous samples are necessary, which makes the conventional procedure laborious and expensive. As an alternative, the apparent electrical conductivity of soil (ECa) can be measured in the field by the use of the electromagnetic induction (EMI) method. This method is fast and allows making extensive ECa determination in space and monitoring. In the present study, an area of 2,060 ha has been investigated in the irrigation district of Tadla, central Morocco. Twelve soil samples were collected for ECe measurement, while 92 ECa measurements were realized with EM38. The pairs of ECe-ECa values allowed establishing the calibration equation permitting to convert the ECa into ECe values and for other ECa values for which ECe was not accomplished. The geostatistics was used to develop maps for the risk of soil salinization. Initially, a threshold for the risk of soil salinization was determined, and indicators were built. Later, the spatial variability of these indicators was described and modelled using the variogram. Finally, the maps were generated based on a non-parametric method of geostatistical interpolation, that is, indicator kriging. The results showed that the study area presents various degrees of soil salinization risks. The south-eastern part and small areas in central west and east of the study area have a low risk of salinization. In contrast, the south-western, the north-western and the central parts have a high risk of salinization. All the remaining parts of the study area have a moderate risk of salinization. It is concluded that the combined use of ECe and ECa-EM38 values and geostatistics allowed establishing a reliable soil salinization risk map and help to develop rehabilitation plan for the salt-affected soils.