kPa are kilopascal 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, though displayed fixed on the IoTUI. To read the thresholds according to your soil type, we have put together a handy visual to use below.
| Soil Texture | Field Capacity (%) | PWP (%) | Field Capacity (kPa) | Upper Optimal (kPa) | Lower Optimal (kPa) | Stress (kPa) |
|---|---|---|---|---|---|---|
| Clay | 35,7 | 30 | 15 | 40 | 60 | 100 |
| Silty Clay | 34,85 | 27 | 20 | 35 | 50 | 70 |
| Sandy Clay | 30,6 | 25 | 20 | 35 | 50 | 70 |
| Clay Loam | 30,6 | 22 | 25 | 40 | 60 | 100 |
Silty Clay Loam | 23,65 | 22 | 20 | 35 | 50 | 70 |
Sandy Clay Loam | 30,6 | 17 | 20 | 35 | 50 | 70 |
| Loam | 26 | 14 | 20 | 35 | 50 | 70 |
| Silt | 25,5 | 6 | 20 | 35 | 50 | 70 |
| Sandy Loam | 17 | 8 | 10 | 30 | 45 | 60 |
| Loamy Sand | 14 | 5 | 15 | 30 | 45 | 60 |
| Sand | 10 | 5 | 10 | 30 | 40 | 50 |