As an appendix to the Harmonized World Soil Database (HWSD) v1.1, seven soil indicators have been published globally, at 5 arc-minute (10 km) resolution. Naturally, we carefully fed it into our mapping tools, and here you can try it out.
From the HWSD website: On the basis of soil parameters provided by HWSD seven key soil qualities important for crop production have been derived, namely: nutrient availability, nutrient retention capacity, rooting conditions, oxygen availability to roots, excess salts, toxicities, and workability... Soil qualities are related to the agricultural use of the soil and more specifically to specific crop requirements and tolerances. For the illustration of soil qualities, maize was selected as reference crop because of its global importance and wide geographical distribution.
The seven indicators are:
- Nutrient availability: Soil texture, soil organic carbon, soil pH, total exchangeable bases
- Nutrient retention capacity: Soil organic carbon, soil texture, base saturation, cation exchange capacity of soil and of clay fraction
- Rooting conditions: Soil textures, bulk density, coarse fragments, vertic soil properties, and soil phases affecting root penetration and soil depth and soil volume
- Oxygen availability to roots: Soil drainage and soil phases affecting soil drainage
- Excess salts: Soil salinity, soil sodicity, and soil phases influencing salt conditions
- Toxicity: Calcium carbonate and gypsum
- Workability (constraining field management): Soil texture, effective soil depth/volume, and soil phases constraining soil management (soil depth, rock outcrop, stoniness, gravel/concretions, and hardpans)
Each of the seven layers qualitatively represents the status of soil quality for a given grid cell:
- no or slight constraints
- moderate constraints
- severe constraints
- very severe constraints
- mainly non-soil
- permafrost area
Although not quantitative, these indicators can be used as a starting point to estimate the soil-inherent abiotic constraints.
The data can be downloaded from the HWSD website and the widget in this post shows the location-specific preview of the dataset. For sub-Saharan Africa region, the boundary of Soil Mapping Unit was overlaid to help understand the spatial extent of areas under the same constraint.
- Fischer, G., F. Nachtergaele, S. Prieler, H.T. van Velthuizen, L. Verelst, D. Wiberg, 2008. Global Agro-ecological Zones Assessment for Agriculture (GAEZ 2008). IIASA, Laxenburg, Austria and FAO, Rome, Italy. (http://www.iiasa.ac.at/Research/LUC/External-World-soil-database/HTML/SoilQualityData.html?sb=11)