Tracking Soil Loss Through Water-Clarity Sensors

Putting a turbidity sensor in crop fields may lead to better monitoring and estimating of soil being lost to water runoff, according to an Agricultural Research Service (ARS) scientist. Turbidity is a measure of suspended particles that diminish water's clarity.

According to agronomist Seth Dabney in the ARS Upland Erosion Processes Research Unit at Oxford, Miss., the sensors may enable researchers and farmers to keep continuous records on soil loss.

The optical sensor measures water clarity by using a light beam that scatters when it strikes suspended particles. Similar devices are used for monitoring the cloudiness of storm runoff, wastewater and waters near construction projects.

Dabney has tested the devices on agricultural fields ranging in size from just under half an acre to 40 acres, placing 28 of them in pipes that discharge precipitation and irrigation runoff. Stationing them at the outlet of fields gives a far more accurate account of sediment flow than placement in a stream or river, where sediment from other fields and areas muddles accuracy.

Measuring runoff rate and periodically collecting either a single composite sample or several sequential samples is the typical way to determine soil loss. Use of this high-quality turbidity sensor for the research costs less than collecting and analyzing numerous runoff samples, and is less labor-intensive.

Dabney's study evaluated turbidity measurements as a means of monitoring soil loss, and explored procedures for improving the reliability of predictions based on soil and flow characteristics.

ARS is the U.S. Department of Agriculture's chief scientific research agency.