Field Capacity and Wilting Point Determination
Field capacity is the amount of water that a soil retains after gravity has pulled away excess water. Wilting point is the moisture content in a soil at which plants would wilt permanently. To determine these values, a moisture analysis is conducted.
How to Do Moisture Analysis?
The field capacity and wilting point of a soil sample can be determined using the following steps:
Materials
- Soil sample
- Pressure plate apparatus
- Water
- Vacuum pump
- Drying oven
Procedure
Determining Field Capacity
- Place a known mass of air-dry soil into the pressure plate apparatus.
- Saturate the soil with water and apply a pressure of 1/3 bar (33 kPa) to the sample.
- Maintain the pressure for 24 hours.
- Remove the pressure and weigh the sample.
- Calculate the field capacity as the percentage of water retained.
Determining Wilting Point
- Place a new sample of air-dry soil into the pressure plate apparatus.
- Apply a pressure of 15 bars (1500 kPa) to the sample.
- Maintain the pressure for 48 hours.
- Remove the pressure and weigh the sample.
- Calculate the wilting point as the percentage of water retained.