Tensiometer Irrigation & Irrigate Now or Hold?

A tensiometer measures soil moisture tension — the suction, in kilopascals (kPa) or centibars, that roots must overcome to pull water from the soil. A low reading means the soil is wet and water is freely available; a high reading means the soil is drying and water is harder to extract. It reads how thirsty the soil is, not how much water it holds.

It depends on soil texture. Sandy soils release water at low tension and dry quickly, so you irrigate at a low threshold (around 10–30 kPa); loams sit in the middle (around 30–50 kPa); clays hold water more tightly and can wait for higher tension (around 50–70 kPa). The tool picks the right irrigate-at threshold for your soil.

It compares your reading to the irrigate-at threshold for your soil texture. If the reading has reached or passed the threshold, it says irrigate; if it's still below, it says hold and shows the margin — how many kPa of drying are left before you need to water.

The same tension represents different amounts of available water in different soils. Sandy soils have little buffer and most of their water leaves at low tension, so waiting risks stress; clays hold a large reserve that only releases as tension climbs, so they can safely dry further before irrigation is needed.

The margin is the gap between your current reading and the irrigate-at threshold. A large positive margin means the soil is still comfortably moist and you can wait; a small margin means irrigation is due soon; a negative margin (past the threshold) means you're already in the irrigate zone and the crop may be drawing on its reserves.

Place it in the active root zone, in a representative part of the field, away from the edge of the wetted pattern of drippers or sprinklers. Many growers use two depths — a shallow one to time irrigation and a deeper one to confirm water reached the lower roots. Keep the ceramic tip in good contact with the soil.

Not always immediately, but a reading well past the irrigate-at threshold means roots are working hard for water and yield can suffer if it continues. Different crops tolerate different tensions; sensitive crops and shallow-rooted vegetables want irrigation at lower tension than deep-rooted, drought-tolerant field crops.

Yes — many electronic soil moisture sensors report in kPa or centibars, the same units as a tensiometer, so you can enter their reading the same way. Capacitance probes often report volumetric percent instead; for those, use the Soil Water Holding Capacity tool to relate moisture to the refill point.

It tells you whether to irrigate now from a single reading, which is the everyday decision. For planning how much to apply and how long between irrigations across the season, combine it with the Irrigation Scheduling and Soil Infiltration tools so you know both when to water and how much.