How do I read soil water potential (kpa) in relation to soil types?

kpa are kilopasquale and the unit of measurement for soil suction which is used to measure the water potential.

Range of water potential

The range of the sensor to capture water potential is 0 to -252. On this scale, 0 would display a state in which the sensor is put in a glass or bucket of water. If you were to stick the sensor in a bucket of sand and continually applied heat, you would see measurements of -252 kpa, meaning completely dry.

What is the impact of soil on water potential?

The interpretation of water potential must always be in relation to the soil type the sensor is placed in. This means that a given measurement, e.g. -35 kpa, has a different meaning from one soil type to another.  

Water potential thresholds by soil type

Depending on your soil type, the thresholds of field potential, upper optimal, lower optimal and stress level will be different. To read the thresholds according to your soil type, we have put together a handy table to use below. 

Soil TextureField Capacity (%)PWP (%)Field Capacity (kpa)Upper Optimal (kpa)Lower Optimal (kpa)Stress (kpa)
Silty Clay34,852720355070
Sandy Clay30,62520355070
Clay Loam30,622254060100

 Silty Clay Loam


Sandy Clay Loam

Sandy Loam17810304560
Loamy Sand14515304560

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