Non-invasive field measurements of soil water content using a pulsed 14 MeV neutron generator

Current techniques of soil water content measurement are invasive and labor-intensive. Here, we demonstrate that an in situ soil carbon (C) analyzer with a multi-elemental analysis capability, developed for studies of terrestrial C sequestration, can be used concurrently to non-invasively measure the water content of large-volume (∼0.3 m3) soil samples. Our objectives were to investigate the correlations of the hydrogen (H) and oxygen (O) signals with water to the changes in the soil water content in laboratory experiments, and in an agricultural field. Implementing prompt gamma neutron activation analyses we showed that in the field, the signal from the H nucleus better indicates the soil water content than does that from the O nucleus. Using a field calibration, we were able to use the H signal to estimate a minimum detectable change of ∼2% volumetric water in a 0–30 cm depth of soil.

► Soil-water content is measured non-invasively in an agricultural field. ► Employs prompt gamma ray neutron activation analysis with pulsed 14 MeV neutrons. ► Hydrogen signal intensity is best indicator of soil water to a depth of 30 cm. ► Mobile system offers potential for quick analysis of a large tract of land in a day. ► Switchable neutron source makes it radiologically safe for storage and transport.