Soil Moisture Sensors for Irrigation Scheduling

Start from the soil and the maintenance you can live with. Medium to heavy soils suit the Irrometer SR (0-100 cb). Coarse and sandy soils and potting media suit the LT (0-40 cb), and small containers and pots the MLT. The SR and LT are supplied in six lengths from 15 to 120 cm, so the depth is set by the length you order. When you want many stations with no refilling, the Watermark 200SS covers the same job with a wider 0-200 cb range and a 5+ year life.

Both read soil water tension, the force roots work against, which is why both schedule irrigation without soil-specific calibration. A tensiometer measures it directly through a water-filled tube and reads the wet range on a gauge, but the tube needs periodic refilling. The Watermark 200SS reads tension through a granular matrix: coarser (±15% of reading between 10 and 100 cb), but maintenance-free, 0-200 cb, and it lasts multiple seasons in the ground.

Tension sensors do not. A tensiometer and a Watermark 200SS read the same physical quantity in any soil, so the irrigation thresholds you set transfer between fields. Volumetric sensors (capacitive, TDR) report water content, which means a soil-specific calibration if the number has to be accurate rather than relative. That difference is the main reason tension sensors are the practical default for irrigation scheduling.

At the depth where the crop takes most of its water, and usually at a second, deeper point to confirm water reaches the bottom of the root zone without passing below it. Shallow vegetables and turf: 15-30 cm. Field crops and mid-depth orchards: 45-60 cm. Deep-rooted trees and vines: 90-120 cm. Watermark sensors are often installed at two or three depths on the same station.

One station per homogeneous irrigation zone (same crop, same soil, same drip line), usually with two depths per station. Start with one or two stations in the most representative zones and expand after a season, once you can see where the real variability is. The system is modular, so later stations join the same controller and dashboard.

Roots need air as much as water. In heavy soils, on high-frequency drip, and in substrate beds, the root zone can stay wet enough to suffocate roots while the moisture reading still looks fine. The O2-100 reads oxygen in the root zone directly (0-25 %VOL), which catches waterlogging and compaction before yield does.

Yes. The Irrometer tensiometers are read on a mechanical gauge as standard; for the SR and LT, Irrometer offers transducers that replace the gauge (ask us about availability). The electronic sensors here connect to an Agrinovo Genesis controller, which logs the readings to the cloud, sends alerts when a zone dries past your threshold, and can open and close valves on the tension reading. It all runs through the IoT soil monitoring platform.

It depends on the sensor type, the number of stations and depths, and whether you read a gauge on field rounds or connect everything to a controller for continuous logging and alerts. Our pricing is by tailored quotation, so you pay for the configuration that fits the plot. Request a quote with your crop, soil type and plot layout and we will come back with a concrete recommendation.