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Redefinition of new Rooting Depth classes

Analysis of available information in the SGDBE - Attribute ROO

In the SGDBE, the attribute ROO gives the depth of an obstacle to roots following 6 classes (Table 6-4).

Table 6-4: ROO classes of the SGDBE and corresponding rooting depth classes in CGMS

The ROO class 6 was introduced for the extension to Mediterranean countries. For the other countries, as the class 6 did not exist, for some soil types, like Lithosols, some country experts chose to use the ROO class 4 for soil types that have an obstacle to roots between 0 to 20 cm. The class 4 must be used with care in this context.

For STUs having an original soil name in the FAO-UNESCO 1974 legend and ROO not equal to 0, we compared the current CGMS rule with the value taken by the attribute ROO (Table 6-5). Note that each individual record is not compared separately. First, all records of the CGMS rule have been applied. Thus, for example, not all soils with phase is ‘flooded’ will receive value ‘3’, only the STUs that have not been assigned ‘1’, ‘2’ or ‘3’ on the basis of previous records like ‘I**’, ‘rO’ etc.

Table 6-5: ROO values for each occurrence of the current CGMS rule for rooting depth for STUs with an original soil name in FAO-UNESCO 1974 legend (in % of the number of STUs by occurrence)

There are good correlations between the occurrences of the current CGMS rule and ROO for 23 occurrences (in bold) over 37. For 10 occurrences (in bold italic light grey), the correlation is medium. There are no corresponding STUs for 4 occurrences. But, only 6 occurrences have a good estimation of rooting depth (underlined) and for 27 occurrences the estimation of rooting depth is bad and often underestimated. The last occurrence has a good correlation with ROO (79%) but represents 1110 STUs that means that 21% of these STUs have a bad estimation which represents more than 230 STUs. It seems important to detail this last occurrence.

The lithic and petrocalcic phases that represent a high constraint to roots have a high variability of ROO that confirms the imprecision of the information given by the phases. The occurrences with slope have a medium correlation. It seems that they don’t give very precise information about rooting depth. It is proposed to drop slope from the rule.

For STUs having an original soil name in the FAO-UNESCO 1974 legend and ROO not equal to 0, the rule that estimates the depth to rock in the current knowledge base of the SGDBE with the value taken by the attribute ROO (Table 6-6) was also compared.

Table 6-6: ROO values for each occurrence of the current DR rule from the knowledge base of the SGDBE (for depth to rock estimation) for STUs with an original soil name in FAO-UNESCO 1974 legend (in % of the number of STUs by occurrence).

There are good correlations between the occurrences of the Depth to Rock (DR) rule and ROO for 37 occurrences (in bold) over 53. For 12 occurrences (in light grey), the correlation is medium. There are no corresponding STUs for 4 occurrences. But, 28 occurrences have a good estimation of rooting depth (underlined) and for 21 occurrences the estimation of rooting depth is bad and often underestimated. Globally, the DR rule seems to estimate better the rooting depth than the CGMS rule. It can be used to give more detail to the last occurrence of the CGMS rule.

The introduction of parent material gives a good improvement of the rooting depth estimation in some cases (especially with carbonated rocks like for Bk or Lo soils). So it is proposed to introduce the parent material information in the rooting depth rule for CGMS.

The lithic phase presents a high variability of ROO classes, especially when it appears as secondary phase.

When the value for ROO attribute is missing or takes the value 1 (no obstacle to roots between 0 and 80 cm), we must use other attributes to estimate the rooting depth class, like TEXT_DEP_ CHANGE and IL that gives information about the subsoil, and the soil name that could give information about the soil depth.

 

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MARS STATEuropean Commission Directorate General Joint Research CentreIES - Institute for Environment and Sustainability IPSC - Institute for the Protection and Security of the Citizen