Determination Of The Water Holding Capacity Of The Soil

Water Holding Capacity

The water-holding capacity (WHC) is defined as the amount of water held in the soil after the excess
gravitational water has drained away and after the rate of downward movement of water has
materially ceased. Stage of field capacity is attained in the field after 24 to 72 hours of saturation; this
is the upper limit of plant-available soil moisture. We must distinguish between soil water content,
(the percent water on an oven-dry weight basis), and the soil water potential (the energy status of
water in the soil), which is usually expressed in pressure units (Pascal or bar). However, as indeed we
are dealing with a tension – a negative pressure – units are usually considered to be negative.


Polythene sheets
Soil auger
Moisture boxes/cans
Ring stand

Funnel (glass or plastic)
Tubing (to attach to bottom of funnel)
Clamp (to secure tubing)
Filter paper (to line funnel)
Beakers (250-mL)
Graduated cylinder
Stirring rod (long)


A. Field Processing

  1. Select a uniform plot measuring (5 m x 5 m) and make a flat and horizontal area.
  2. Remove any loose material from the surface (weeds, pebbles, etc.).
  3. Make bunds around the plot.
  4. Fill sufficient water in the plot to completely saturate the soil.
  5. Cover the plot area with a polythene sheet to check evaporation.
  6. Take soil sample from the centre of the plot from the desired layer, starting after 24 h of
    saturation and determine moisture content daily till the values of successive days are nearly
  7. Record the weight of the oven-dry soil.
  8. Repeat above on next day and so on till a constant oven-dry soil value is reached.

B. Laboratory Processing

  1. Thoroughly air-dry compost and soil samples.
  2. Attach and clamp tubing to bottom of funnel and attach funnel to ring stand.
  3. Place filter paper in funnel.
  4. Fill funnel with the 100 mL sample – do not compact.
  5. Measure out 100 mL of water using the graduated cylinder.
  6. Gradually add water to the sample until covered. Record the amount of water added.
  7. Stir gently and let sit until sample is fully saturated.
  8. Release the clamp and collect excess water in the graduated cylinder (water drained, mL).
  9. Record the amount of water in the cylinder.
  10. Calculate how much water was retained in the 100-mL sample of compost, soil or compost/
    soil mixture and then calculate the water-holding capacity.


Technical Remarks

  1. Estimates of soil WHC, wilting point and texture can be made from the saturated moisture
  2. Plot the daily readings on a graph paper. The lowest reading is taken as the value of field
    capacity of the soil.

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