Development and field evaluation of a horizontal pneumatic sensor equipped with multiple nozzles for on-the-go soil mechanical strength measurement

The compaction of agricultural soils is the main limitation to crop roots, leading to reduced yields for most agronomic crops. Soil compaction alters soil structure and limits water and air infiltration. The vertical penetrometer is commonly used to measure soil resistance, but it is time-consuming, costly, and challenging, which has limited its use in soil compaction mapping in vast fields. One of the methods introduced in the last decades is a continuous and on-the-go system to determine the compacted soil layer. This study aimed to measure the mechanical strength of soil at different soil depths using an on-the-go horizontal pneumatic sensor designed and fabricated. The stress calculations for the tine were performed first, followed by a stress analysis of the proposed tine stem using ANSYS software. Then, three conical nozzles at three depths (15, 30, and 45cm) were installed on the pneumatic sensor tine to inject airflow into the soil, and three pressure gauges measured the resistance to air permeability into the soil. The sensor was tested and compared with the standard vertical penetrometer in three replications. The comparison results specified that the sensor could show different soil compactions at various depths, even where a vertical penetrometer could not penetrate the soil. There was a significant relationship between the mechanical strength of soil and vertical penetration resistance (R2=0.73) at depths of 0-30cm. The air permeability resistance in the soil increased with the soil depth.