Multi-frequency electromagnetic induction soil moisture characterization under different land uses in western Newfoundland

Identifying and characterizing the spatial patterns in soil moisture variability under different land use conditions is crucial for agriculture, forestry, civil and environmental engineering. Yet employing multi-frequency electromagnetic induction (EMI) techniques to carry out this task is under-represented in boreal podzolic soils. This study: (i) compared four frequencies (2.8 ~ 80 kHz) for shallow mapping of soil moisture measured with a time-domain reflectometry at 0 – 20 cm soil depth under three different land-use conditions (agricultural land, field road, and a recently cleared natural forest), (ii) developed a relationship between apparent electrical conductivity (ECa) measured using multi-frequency EMI (GEM-2) and soil moisture and (iii) assessed the effectiveness of ECa as an auxiliary variable in predicting soil moisture variations under different land use conditions. The means of ECa measurements were calculated for the exact sampling location (ground truth data) in each land use condition at a research site, Pasadena, Newfoundland. Soil moisture–ECa linear regression models for the three land-use conditions were only statistically significant for 38.3 kHz frequency and were further analyzed. Further statistical analysis revealed that ECa was primarily controlled by soil moisture for the three land-use conditions, with the natural forest possessing the highest mean ECa and soil moisture. Geostatistical analysis revealed that cokriging ECa with less densely collected soil moisture improved the characterization accuracy of soil moisture variability across the different land use conditions. These results reveal the effectiveness of the georeferenced MF–EMI technique to rapidly assess intra-field soil moisture variability under different land uses.