The SMP buffer procedure is used to determine the lime requirement of a soil. Five grams of soil are wetted and allowed to sit for thirty minutes. 10 ml of SMP buffer solution are added and periodically stirred. After 25 minutes, the pH of the soil is measured. Approximately five minutes are need to prepare and analyze each sample, plus a total of one hour of wait time for each batch. 

Principle

The SMP buffer procedure is used to determine the lime requirement of a soil. Five grams of soil are used for each sample. Approximately five minutes are need to prepare and analyze each sample, plus a total of one hour of wait time for each batch. 

Equipment

  • Sample holder (beaker or Falcon tube with lid
  • Stir rod (if using beaker)
  • Hanna HI5522 pH meter 

Reagents

  • pH calibration buffers
  • SMP buffer solution
  • DI water

Procedure

  1. Measure 5 g of soil into a beaker or Falcon tube.
  2. Add 5 ml of DI water.
  3. Stir and let sit for 30 minutes.
  4. Calibrate the pH meter according to the instructions on the screen. If measuring pH is desired, and the soil is appropriate for a 1:1 ratio measurement, measure the pH now.
  5. Add 10 ml of the SMP buffer solution, and stir every 5 minutes for the next 20 minutes. Immediately after the final stirring, insert the pH probe and record the measurement once it stabilizes. Be sure to measure the pH between 20 and 25 minutes after the addition of the SMP buffer.
  6. Rinse the electrode and pat dry between readings.