ROOTS (Obstacle to Roots): Provides the depth class of an obstacle to roots within the STU Code Obstacle to roots (ROO) 0 No information 1 No obstacle to roots between 0 and 80 cm 2 Obstacle to roots between 60 and 80 cm depth 3 Obstacle to roots between 40 and 60 cm depth 4 Obstacle to roots between 20 and 40 cm depth 5 Obstacle to roots between 0 and 80 cm depth 6 Obstacle to roots between 0 and 20 cm depth

ISSOIL (Flag for non-soil units). Field indicating if the soil mapping unit is a soil or a non-soil. CODE ISSOIL 0 Non-soil unit 1 Soil

Reference depth of the soil unit. Reference soil depth of all soil units are set at 100 cm, except for Rendzinas and Rankers of FAO-74 and Leptosols of FAO-90, where the reference soil depth is set at 30 cm, and for Lithosols of FAO-74 and Lithic Leptosols of FAO-90, where it is set at 10 cm6 . An approximation of actual soil depth can be derived through accounting for relevant depth limiting soil phases, obstacles to roots and occurrence of impermeable layers (the latter two refer to ESDB only).

Reference Bulk Density of topsoil.Reference bulk density is a property of particulate materials. It is the mass of many particles of the material divided by the volume they occupy. The volume includes the space between particles as well as the space inside the pores of individual particles. The calculation procedures for reference bulk density can be found at http://www.pedosphere.com/resources/bulkdensity/index.html Bulk density, as a soil characteristic, is a function rather than a single value (USDA-NRCS, 2004 #3078, p. 73) as it is highly dependent on soil conditions at the time of sampling: changes in (field) water content will alter bulk density. The SOTWIS database provides estimates of bulk density values derived from available analyzed data, and thus consider differences in soil texture, organic matter content and porosity. Careful review of these values also by comparison with calculated reference bulk densities has revealed substantial differences. For reasons of data quality and consistency of the HWSD, reference bulk density values – calculated using equations developed by Saxton et al. (1986), have been used here: these equations represent a statistical estimate and reflect only the textural influence.

This field gives the percentage of organic carbon in the subsoil. Organic Carbon is together with pH, the best simple indicator of the health status of the soil. Moderate to high amounts of organic carbon are associated with fertile soils with a good structure. Soils that are very poor in organic carbon (<0.2%), invariable need organic or inorganic fertilizer application to be productive. Soils with an organic matter content of less than 0.6% are considered poor in organic matter. The following classes are suggested to prepare maps of organic carbon status for mineral soils: Code Percentage organic carbon 1 < 0.2 2 0.2 – 0.6 3 0.6 – 1.2 4 1.2 – 2.0 5 > 2.0

This field gives the percentage of organic carbon in the subsoil. Organic Carbon is together with pH, the best simple indicator of the health status of the soil. Moderate to high amounts of organic carbon are associated with fertile soils with a good structure. Soils that are very poor in organic carbon (<0.2%), invariable need organic or inorganic fertilizer application to be productive. Soils with an organic matter content of less than 0.6% are considered poor in organic matter. The following classes are suggested to prepare maps of organic carbon status for mineral soils: Code Percentage organic carbon 1 < 0.2 2 0.2 – 0.6 3 0.6 – 1.2 4 1.2 – 2.0 5 > 2.0

Volume percentage gravel respectively in the subsoil. Gravel stands for the percentage of materials in a soil that are larger than 2 mm.

On the basis of soil parameters provided by the Harmonized World Soil Database (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. Workability (SQ7) Diagnostic characteristics to indicate soil workability vary by type of management applied. Workability or ease of tillage depends on interrelated soil characteristics such as texture, structure, organic matter content, soil consistence/bulk density, the occurrence of gravel or stones in the profile or at the soil surface, and the presence of continuous hard rock at shallow depth as well as rock outcrops. Some soils are easy to work independent of moisture conditions, other soils are only manageable at an adequate moisture status, in particular for manual cultivation or light machinery. Irregular soil depth, gravel and stones in the profile and rock outcrops, might prevent the use of heavy farm machinery. The soil constraints related to soil texture and soil structure are particularly affecting low and intermediate input farming LUTs, while the constraints related to irregular soil depth and stony and rocky soil conditions are foremost affecting mechanized land preparation and harvesting operations, of high-level input mechanized farming LUTs. Workability constraints are therefore handled differently for low/intermediate and high inputs. The workability soil quality SQ7 includes physical hindrance to cultivation, and limitations to cultivation imposed by texture/clay mineralogy. The soil quality SQ7 is derived by combining the most limiting soil/soil phase attribute with the average of the remaining attribute coditions. Soil phases considered in the quantification of SQ7 are stony, lithic, petric, petrocalcic, petroferric, fragipan and duripan (FAO ‘74), and lithic, petroferric, rudic, skeletic, duripan and fragipan (FAO’90). Note that the classes used in the Soil Quality evaluation are: 1: No or slight limitations 2: Moderate limitations 3: Sever limitations 4: Very severe limitations 5: Mainly non-soil 6: Permafrost area 7: Water bodies Remember that classes are qualitative not quantitative. Only classes 1 to 4 are corresponding to an assessment of soil limitations for plant growth. Class 1 is generally rated between 80 and 100% of the growth potential, class 2 between 60 and 80%, class 3 between 40 and 60%, and class 4 less than 40%.

Percentage sand in the in the subsoil. Sand comprises particles, or granules, ranging in diameter from 0.0625 mm (or 1⁄16 mm) to 2 millimeters. An individual particle in this range size is termed a sand grain. Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour). Sand is commonly divided into five sub-categories based on size: very fine sand (1/16 - 1/8 mm diameter), fine sand (1/8 mm - 1/4 mm), medium sand (1/4 mm - 1/2 mm), coarse sand (1/2 mm - 1 mm), and very coarse sand (1 mm - 2 mm).

This field gives the soil reaction of top- and subsoil. pH, measured in a soil-water solution, is a measure for the acidity and alkalinity of the soil. Five major pH classes are considered here that have specific agronomic significance: pH < 4.5 Extremely acid soils include Acid Sulfate Soils (Mangrove soils, cat clays). Do not drain because by oxidation sulfuric acid will be produced and pH will drop lower still. pH 4.5 – 5.5 Very acid soils suffering often from Al toxicity. Some crops are tolerant for these conditions (Tea, Pineapple). pH 5.5 –7.2 Acid to neutral soils: these are the best pH conditions for nutrient availability and suitable for most crops. pH 7.2 – 8.5 These pH values are indicative of carbonate rich soils. Depending on the form and concentration of calcium carbonate they may result in well structured soils which may however have depth limitations when the calcium carbonate hardens in an impermeable layer and chemically forms less available carbonates affecting nutrient availability (Phosphorus, Iron). pH > 8.5 Indicates alkaline soils often highly sodic (Na reaching toxic levels), badly structured (columnar structure) and easily dispersed surface clays.