Both tests rely on good soil sampling methods to get a representative sample of each soil type in a paddock. Know the critical pH of the species grown. Consider what species of plants you grow. The pH of your topsoil and subsoil should be above the critical pH of the most acid sensitive crop you grow otherwise pH will limit production. If pH is limiting production, then liming is likely to be a profitable option.
Different plants have different tolerances to acidity.
Plant growth is affected at a certain soil pH, this is called the critical pH and is often given as a range. Below the critical pH, plants do not take up soil nutrients efficiently and will suffer yield penalties. Acidity is insidious, yield penalties of 20 - 30 per cent build up gradually and may not be noticed if agronomy is improved in other ways. See Figure 5 for the critical topsoil pH points of WA crops, but note that some crops such as pulses need a higher subsoil pH. Figure 5. Image Legend for Figure 5.