Rewriting PTR salinity, alkalinity, chemical toxicity and drainage based on the wrb-standard
Description of the current salinity rule
The current rule used for estimating salinity in CGMS is described in Table 4-1.
When analysing this rule, it appears that the rule considers four categories of soils:
- soils having a low amount of salt;
- soils having a high amount of salt (Solonchaks (FAO-UNESCO 1974 legend));
- soils having a high amount of gypsum which can be toxic for plants (Gypsic soils (FAOUNESCO 1974 legend));
- soils having a high amount of sulphur which can be toxic for plants (Thionic Fluvisols (FAOUNESCO 1974 legend)).
The last two categories can lead to confusion when using the PTR salinity for other purposes than CGMS. So we propose to create two distinct rules, one for salinity, the other for toxicity to plants, in the knowledge base of the SGDBE version 4.0. For CGMS only (in its present state), the results of these two rules will be merged into a unique variable in respect to the present structure of CGMS.
Salinity of soil can prevent plants to take water from soil. It is measured by the electrical conductivity of the saturation extract in dS/m at 25°C (ECse). The tolerance to salt is different from one crop to another. The threshold for salinity tolerance (mean of salinity within rooting depth) varies from 1.3 dS/m for the more sensitive crops to 10 dS/m for the more tolerant ones.