Assessing new sensor-based volume measurement methods for high-throughput bulk density estimation in the field under various soil conditions

Soil bulk density (BD) is a key soil property in soil science. BD is measured at the scale of the soil horizon with conventional methods: core sampling and rubber balloon. Regardless of the method, BD measurement in the field is cumbersome and time consuming, especially in stony soils, and new, less invasive methods have emerged, but their measurement quality needs to be compared with conventional methods. The photogrammetric technique (SfM) consists of the reconstruction of a given scene in 3D from multi-view photographs. The aim of the present work is to assess the SfM as a rapid, accurate method of measuring the volume of undisturbed soil for BD measurements, regardless of the soil depth and stone content. Ten soil horizons were investigated from various types of soils with different soil properties, especially texture (10 to 48% of clay) and stone content (0 to 73%). The bulk density of each horizon was measured with a reference method (core sampling), an excavation method (rubber balloon) and two recently developed sensor-based methods: SfM and a lightweight flash LiDar. For the sensor-based methods, an automated post-processing method was developed to reduce the human operating time. The BDs measured from the SfM were significantly similar to those measured from core sampling. At this stage, the lightweight flash LiDar is not sufficient to measure the BD with high accuracy. Finally, we recommend the use of SfM to measure BD regarding its robustness in varying soil conditions, especially stony soils, and we discuss the potential of the method regarding the recent advances in its field use with smartphones. Highlights Soil bulk density (BD) is a key soil property in soil science The photogrammetric technique and flash Lidar were applied to measure BD in the field The photogrammetric technique and flash Lidar were compared to classical methods The flash lidar is not sufficient to measure the BD with high accuracy The photogrammetric technique is recommended especially in stony soils

Automated summary

The study evaluated the photogrammetric technique (SfM) as a rapid, accurate method of measuring undisturbed soil volume for bulk density (BD) measurements. The results showed that the BD measured by SfM was significantly similar to that measured by core sampling, indicating the suitability of SfM for stony soils.