Site-specific measurements of apparent electrical conductivity (ECa) correlate to neutron moisture probe counts: Towards the spatial measurement of soil moisture content for precision agriculture

Precision management of broad acre cropping is limited by our inability to rapidly produce high spatial-resolution maps of soil moisture. We report on a series of site-specific, apparent electrical conductivity (ECa) measurements using the Geonics® EM38 along with near-simultaneous neutron probe measurements during soil moisture extraction by an irrigated cotton crop. This study differs from previous approaches by using polyethylene neutron probe access tubes so that the EM38 could be operated directly over the soil measured by the neutron probe. We discover strong correlations (average R²= 0.90) between ECa and neutron probe counts (NPC) that suggest that ECa surveys could provide a useful spatial measure of soil moisture. The linear relationships between NPC and ECa across a range of background ECa zones for these soils augers well for estimating site-specific moisture content from the coefficient of slope and a site-specific upper limit to ECa representing field capacity (i.e. full point).