CropX: Spiral soil sensor delivers best accuracy

Ag analytics and soil sensing company CropX released results of a multiyear study on the impact of soil sensor geometry and installation method on moisture readings and irrigation. The study found that spiral sensor designs deliver the best accuracy.

Preferential flow in soil

“The occurrence of preferential flow in soil is well documented,” noted Guy Sela, CropX VP of Agronomy. “The geometry of the soil sensor and the installation method greatly affect the accuracy of soil moisture readings as most sensors relay information based on preferential flow rather than the true moisture level in the soil. Spiral sensors offer the most accurate view of the actual moisture content of undisturbed soil in the field.”

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Spiral sensors

The study modeled the formation of preferential flow pathways around sensors with different geometries and quantified the difference between the soil moisture in undisturbed soil and the soil moisture reported by the sensors. Across different soil types (e.g., loamy, sandy, silty), soil depths and irrigation amounts/intervals, the study found that spiral sensors moisture readings mapped most closely to undisturbed soil.

Key findings

• Spiral sensors agreed most closely with undisturbed soil moisture readings after irrigation;
• Tube and fork sensors exhibited a false “spike” in moisture readings immediately following irrigation compared to undisturbed soil;
• The disturbed soil near the tube and fork sensors also caused the average moisture (moisture between irrigation events) to rise after each irrigation event – leading to erroneous moisture readings – up to 10 percent higher volumetric water content (VWC) than the actual soil moisture;
• Tube and fork sensors’ tendency to overestimate the actual soil moisture increased with higher amounts of water;
• The accuracy of tube and fork sensors decreases when large amounts of water are used for irrigation, regardless of soil properties; and
• Spiral sensors outperformed other designs, reporting accurate moisture readings during and between irrigations with no significant deviation based on the amount of water used.

“Spiral sensors offer the most accurate view of the actual moisture content of undisturbed soil in the field – reflecting the true moisture conditions across varying soil types and irrigation events,” added Sela. “It is time for the industry to recognise the critical role of spiral sensors for the next era of smart irrigation and soil health.”