Contents
Where to Position Probes
This guide is focused on placement only. For deciding the number of probes, see the dedicated page: How many probes should you install?.
Related guides
Where to position them
- Always in a representative area of the field, or in the driest part if you must choose only one conservative control point.
- Where root density is high, because the probe should track water that is actually accessible to the crop.
- Inside the irrigated zone: under drippers / between sprinklers depending on the system, never outside irrigated areas.
- In drip irrigation, place the probe on the wet bulb edge, between the emitter and the outer wetting front; closer to the emitter in sandy soils, farther away in clay soils.
- In field crops, probes are generally placed on the row or slightly offset depending on crop; some references indicate around 8 cm from the row for maize and sugar beet, and directly on the row for wheat.
Horizontal positioning matrix
This matrix helps choose horizontal probe placement based on soil type and irrigation method.
| Soil type | Drip irrigation | Sprinkler irrigation | Pivot / lateral move | Localized irrigation under mulch |
|---|---|---|---|---|
| Sandy | In the core of the wet bulb, close to the irrigation line but not directly under the emitter (actual irrigated volume). | Well-covered central area, away from dry edges and poorly irrigated zones. | Sector crossed by the pivot, in a stable area, neither too close nor too far from the arm. | Under the irrigation line, where wetting is most stable, within the active root volume. |
| Silty | In the useful wet volume, neither too close nor too far from the application point, avoiding bulb edges. | Mid-field point in a uniformly covered area, outside over- or under-irrigated zones. | Standard point in the irrigated area, avoid extremes of the distribution curve. | In the soil area actually wetted under the line/mulch, as close as possible to the active root zone. |
| Clay | Slightly offset from the emitter, in the zone where water spreads without accumulating; avoid stagnant points. | Central and stable zone, avoiding crusted areas or stagnation depressions. | Representative area, not in a depression or on a drainage hump, avoid local excesses. | In an area receiving water without prolonged over-wetting, where water remains useful and does not run off. |
Simple rule by situation
| Situation | Recommended placement |
|---|---|
| Uniform field, one crop, one irrigation setup | Representative area, high root density, irrigated zone. |
| Heterogeneous field | One representative (or driest) area in each instrumented zone. |
| Deep-rooted crop | Active root profile, to monitor upper and lower layers. |
| Drip irrigation | Wet bulb edge, not directly under the emitter. |
What we recommend
Start by selecting a representative and irrigated location. Then adjust the number of points according to field heterogeneity with our dedicated guide: How many probes should you install?.
Frequently asked questions
How many probes should I install in one field?
The number depends on field heterogeneity. See our dedicated guide for a clear method: How many probes should you install?.
Which probe length should I choose?
The number of measurement depths should be selected according to crop root depth and your irrigation objective (surface monitoring, available water reserve, or lower-profile verification). To choose the right probe length and depth levels, see our guide: Probe size guide.
Where should a probe be placed in drip irrigation?
Place the probe in the actual irrigated zone, at the edge of the wet bulb, between the emitter and the wetting front limit, not directly under the emitter. The goal is to measure water effectively available to roots, not a locally over-wet point.