Tests included in this section involve calculations using results obtained from methods described earlier in the chapter (Colwell-P and PBI+ColP; Methods 9B and 9I2, respectively), and in Chapter 18 Mehlich 3-P (Method 18F1/18F2), Mehlich 3-Fe (Method 18F1) and Mehlich 3-Al. (Method 18F1). The tests are the Mehlich 3 P Saturation Ratio (M3PSR) and the ratio of Colwell-P/PBI+ColP. Very high levels of 0.005 M CaCl2-extractable P (methods 9F1/9F2) are also indicative of soils with above normal risk of P transport in runoff and leachate. Tentative interpretative criteria are summarised in Table 9.11.
Table 9.11. Tentative interpretative criteria for three soÕ environmental P tests.
Test |
Tentative interpretative criteria |
Reference |
M3PSR {molar ratio of Mehlich 3 extractable P/(Mehlich 3-Fe + Mehlich 3-Al)} |
Environmental P hazard/risk increases sharply above 0.2. |
Maguire and Sims (2002); Bloesch and Rayment (2006); Sims et al. (2006) |
Colwell-P/PBI+ColP Ratio |
Environmental P hazard/risk increases above 2.0. |
|
0.005 M CaCl2 extractable P (methods 9F1/9F2) |
Environmental P hazard/risk increases above 2000 μg P/kg |