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Plant Available Water

Setting the field capacity (FC) value defines the maximum amount of water soil can hold against gravity drainage. Setting the permanent wilting point (PWP) value defines the water content at which plants can no longer extract water from the soil.

Travis Bates
Updated by Travis Bates

 

Setting the field capacity (FC) value defines the maximum amount of water soil can hold against gravity drainage. Setting the permanent wilting point (PWP) value defines the water content at which plants can no longer extract water from the soil. Plant available water (PAW) is expressed as a percent.

The PWP value is set based on soil texture. Published values for PWP and FC are available, however, FC is most often derived in the field by evaluating data. Available water content (AWC) is equal to the water content at field capacity minus the water content at permanent wilting point. See our article How do I determine field capacity and permanent wilting point? to learn more.

Formula

  1. AWC = FC - PWP  
  2. PAW = (VWC - PWP) / AWC  

METER Sensors needed for calculating PAW

  • TEROS Sensors: TEROS 12/ TEROS 11/ TEROS 10
  • ECH2O Sensors: EC-5/ 10HS/ GS1/ GS3

New PAW

  • Click the environmental model icon.
  • Select Plant Available Water.
  • Enter a name for the model and a name for the chart.
  • Select a device.
  • Enter the Field Capacity (FC %) and Permanent Wilting Point (PWP %) values for each trace.
  • Click Create.
Values for the Management Allowable Depletion, % Sand, Clay, Silt and Texture name are optional and do not impact the calculations for PAW.

Edit PAW

  • Click the Edit chart icon.
  • Click the arrow icon to the right of one of the PAW traces.
  • Edit the values.
  • Click the Save button.
  • Click Update.

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