Soil pH and EC are measured in a 2:1 water:soil ratio. The entire process will take about five minutes per sample for preparation and analysis, plus fifteen minutes of shaking time for each batch. 10 g of soil are used for this analysis. One standard check sample is included in each batch.

Principle

Soil pH can be measured at either a 1:1 or 2:1 water:soil ratio. According to NAPT, they are very similar: 1:1 soil-water pH = 0.99 x 1:2 soil:water pH – 0.04

Soil EC can be measured in the field, and lab testing is inherently inaccurate. It is a best practice to measure EC using a probe consistently, at the same time as pH. A 2:1 water : soil ratio is ideal for clayey or heavily organic soils, and if lime requirement is not also being calculated. A 1:1 water : soil ratio is ideal if lime requirement is also being calculated, and is reasonable for soils with a lower clay content. 

Equipment

  • Hanna HI5522 with appropriate probes
  • Small beaker with glass stir rod OR Falcon tube with cap
  • Reciprocating shaker (if using Falcon tube)

Reagents

  • pH calibration standards (4.01, 7.01, 10.01)
  • EC calibration standards
  • DI water

 Procedure

  • Measure 10 grams of soil into the beaker or Falcon tube.
  • Add 20 ml of DI water.
  • Stir frequently or place on a shaker for 15 minutes.
  • Calibrate the pH and EC meter according to the instructions on the screen.
  • Insert rinsed pH, EC, and temperature probes into each sample. To the extent possible, keep the probes still and not against the wall or bottom of the vessels. For the EC probe, the liquid needs to come up to the drain holes or the measurement will be meaningless. This may require the tipping of the vessel, using a vessel that is tall and thin, or decanting the supernatant into a test tube. Record results when the numbers stabilize.
  • When not measuring, make sure that the probes are rinsed and submerged in 3M KCl.
  • Between measurements, rinse each probe well with DI water and gently pat dry.