Technology
Use root-zone moisture, crop stage and soil type to guide irrigation.
A bed can look dry while its root zone still holds water, or seem moist after wind while roots are drying. Check the active root zone, not surface appearance alone.
A watering threshold defines when to begin irrigation. Keep that trigger separate from the stop target, which describes how much of the root zone to replenish.
Sandy soils store less plant-available water and drain faster, so crops may reach stress sooner. Clay stores more total water, but can drain slowly and become waterlogged.
Place measurements where most water uptake occurs. A sensor above the active roots may read dry too soon; one below them can stay wet after the upper zone is depleted.
Seedlings have small root systems, so their surface layer can dry quickly. Expand the monitored zone as roots deepen, and allow less depletion during sensitive stages such as flowering.
Tensiometers measure soil-water tension; capacitance and time-domain reflectometry estimate volumetric water content. Their readings are not interchangeable, so verify them with field checks.
Start when active-root-zone measurements approach the crop’s depletion limit and expected rainfall will not refill it in time. Check weather and crop stage if the reading seems unusual.
Stop when the intended part of the root zone has been replenished. Avoid prolonged saturation or water draining below the roots, and use lower-depth readings as a check.
Start with crop guidance and soil water-holding properties. Record sensor readings alongside irrigation, rainfall and crop stage, then adjust for plant response and field conditions.
The same threshold may not suit every field: texture, calibration, rooting depth, irrigation layout and crop sensitivity vary. Confirm readings with a probe or other field observation.
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