Researchers from New Mexico State University created a new system to measure soil density with just a smartphone and a 3D-printed tool.

Experimental set up showing soil sample on a 3D-printed turntable with cell phone. A light provides consistent illumination while a white background and white turntable top reduce background influence. The soil sample is rotated on the turntable while taking an image every one fourth rotation. Source: Colby BrungardTo determine soil density and to compare nutrient and carbon stocks of various kinds of soil, scientists have to find the weight and volume measurements of a ped, or soil sample. Determining weight is fairly simple using just a scale, while determining volume is more difficult: either coating a ped in wax and placing it in water, which is messy, or using 3D laser scanning, which is expensive and time-consuming.

The team determined that with their new system, the volume can be determined using high-resolution photos of soil peds taken with smartphone cameras. They created a 3D-printed tiny turntable that is just a few inches across, which allowed the team to take consistent photos of all angles of a sample. The turntable has a cradle for a phone to keep it stable while a simple hand crank turns the camera while taking multiple photos at all angles. The photos are then uploaded to a computer program that stitches them together to create a 3D image that gives the volume measurement.

The team compared their smartphone system to laser scanning and wax dipping, and the final measurements were identical in all methods across five types of soil peds. This system takes 15 minutes per sample to analyze, although there is some downtime while the computer program analyzes the images. A laser scan can take up to an hour and a half. Overall the smartphone system is simple, fast, cheap and accurate, according to its developers.

A paper on the new system was published in Soil Science Society of America Journal.