# Rapid Soil Tests for Assessing Soil Health
## 3 Results
### Step 2: Translation or New Calibrations  
An overview of the main current routine soil tests for selected countries is given in Table 3. The number of soil characteristics in a routine soil test package ranges between 4 and 6 for China, Germany, Lithuania, Sweden, and the UK, and exceeds 15 for Finland, France, and the Netherlands. All routine soil tests include P, K, and pH. The essential (main) nutrient sulfur (S) is only included in routine soil tests in the Netherlands. Micronutrients are not routinely analyzed, while some countries (e.g., Vietnam) have no history of routine soil testing and, hence, no formal routine soil tests. The soil indicators used by countries listed in Table 3 often have a different method than used in the soil health indicator discussed in this paper. For these countries, translation functions (see Figure 1, step 2) can be used, to translate the results of the soil health indicator in the pertinent routine soil tests. Since only few soil characteristics are routinely determined in most countries, the translation functions are most important for P, K, and pH. Figure 3: Relationship between soil pH—0.01 M CaCl\({}_{2}\) (\(x\)-axis) and 0.01 M CaCl\({}_{2}\)-extracted nickel (Ni), aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), and lead (Pb) (\(y\)-axis, \(\upmu\) kg\({}^{-1}\)). Soil samples (0–25/30 cm) originate from agricultural, natural, and urban fields in Europe (n = 1886). Olsen phosphorus (P-Olsen), which is used in several countries and included in the EU proposal, can be translated using total phosphorus (P-total) and oxalate-extractable phosphorus (P), iron (Fe), and aluminum (Al), with reported correlations of R\({}^{2}\) > 0.70 [71; 72; 73]. Future translation functions--potentially incorporating P-total, oxalate-extractable P, P-binding capacity (all of which can be assessed using near-infrared spectroscopy (NIRS) [42; 74; 75]), and CaCl\({}_{2}\)-extractable P (P-CaCl\({}_{2}\))--may further improve the accuracy of the translation functions for P-Olsen. For the soil health indicator, both pH measured in CaCl\({}_{2}\) and in water are included. The relationships between these two and pH measured in KCl are well established [76; 77]. Other soil characteristics--though often not part of routine soil testing--can also be translated relatively easily. For example, the relationship between total nitrogen measured via the Dumas method (used in the soil health indicator) and the [PERSON] method is strong, with R\({}^{2}\)\(\geq\) 0.96 e.g., [78]. Several translation functions are available to relate EC 1:5 (used in the Soil Health Indicator) to ECe, as proposed in the EU framework. For example, [PERSON] et al. (2022) [79] reported a model requiring only EC 1:5 and soil texture to estimate ECe, achieving an R\({}^{2}\) of 0.99 and an RMSE of 1.39 dS/m. Similarly, cation exchange capacity (CEC) values show strong agreement across several analytical methods, with correlations R\({}^{2}\) > 0.92 e.g., [80]. Because soil tests for (heavy) metals, bulk density, and biological soil characteristics are relatively new to many national routine soil testing programs, translation functions for these parameters are currently not needed.