Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2001
Publication Date: 8/8/2001
Citation: Clay, D.E., Chang, J., Malo, D.D., Carlson, C.G., Reese, C., Clay, S.A., Ellsbury, M.M., Berg, B. 2001. Factors influencing spatial variability of soil apparent electrical conductivity. Communications in Soil Science and Plant Analysis 32 (19-20): 2993-3008. Interpretive Summary: This research was done to identify factors that influence the spatial variability in readings from instruments that measure soil electrical conductivity. These instruments are expected to find usefulness as a diagnostic tool for precision farming. Soil apparent electrical conductivity can be used as a precision farming diagnostic tool more efficiently if the factors influencing spatial variability of the measurements are understood. We found that conductivity readings changed over the landscape within fields and were influenced by: (i) water leaching salts out of summit areas and by movement of water and salts upward from subsurface to surface soils in toeslope areas; (ii) lower water contents in summit than in toeslope soils; and (iii) transport of surface soil by water erosion from higher areas to lower areas. This research showed that the soil forming processes as well as previous agricultural management can influence electrical conductivity readings. This information also can be used to improve soil sampling strategies.
Technical Abstract: The objective of this study was to ascertain the causes of ECa spatial variability in soils developed in an environment receiving 50 to 65 cm of annual rainfall. Soils at the research sites were formed on calcareous glacial till parent materials deposited about 10,000 years ago. Soil Soil samples (0-15 cm) were collected from a 60 by 60 m grid in 4 fields and were analyzed for Olsen P and K. Elevation was measured by a carrier phase single frequency DGPS and ECa was measured with an EM 38 (Geonics LTD., ON, Canada) multiple times between 1995-1999. Apparent electrical conductivity contained spatial structure in all fields. Generally, well drained soil in summit areas and poorly drained soil in toeslope areas had low and high ECa values, respectively. Landscape differences in ECa were attributed to: (i) water leaching salts out of summit areas and capillary flow combined iwth seepage transporting water and salts from subsurface to surface soils in toeslope areas; (ii) lower water contents in summit than toeslope soils; and (iii) transport of surface soil by water erosion from summit/shoulder areas to lower backslope/footslope areas. A conceptual model was developed in which topography followed a sine curve and ECa followed a cosine curve. Field areas that did not fit the conceptual model were: (i) sites of old animal confinement enclosures; (ii) areas where high manure rates had been applied; and (iii) areas where soils were outside the boundary conditions of the model. This research showed that the soil forming processes as well as agricultural management influenced ECa and that by understanding how landscape position influences salt loss and accumulation, water redistributions following precipitation, and erosion areas that do not fit the conceptual model can be identified.