Protocols for Mapping Soil Salinity at Field Scale: EC a Survey Considerations D.L. Corwin 1 and S.M. Lesch 2 1 USDA-ARS, U.S. Salinity Laboratory Riverside, CA 2 Department of Environmental Sciences University of California Riverside, CA

2 Dynamic Nature of Soil Salinity Soil salinity is dynamic, varying both spatially and temporally. Soil salinity is dynamic, varying both spatially and temporally. Exhibits complex spatial patterns. Exhibits complex spatial patterns. Mapping and monitoring at field scales requires a rapid, reliable, and easy means of taking geospatial measurements. Mapping and monitoring at field scales requires a rapid, reliable, and easy means of taking geospatial measurements.

3 Apparent Soil Electrical Conductivity (EC a ) EC a is a complex measurement, influenced by several soil properties: EC a is a complex measurement, influenced by several soil properties:  salinity  texture  water content  bulk density  organic matter  clay mineralogy  temperature EC a is a fast, reliable, easy-to-take measurement that is easy to mobilize EC a is a fast, reliable, easy-to-take measurement that is easy to mobilize

4 Mapping Field-scale Soil Salinity Apparent soil electrical conductivity (EC a ): Apparent soil electrical conductivity (EC a ):  electrical resistivity (ER) Electrodes Veris 3100

5 Apparent soil electrical conductivity (EC a ): Apparent soil electrical conductivity (EC a ):  electrical resistivity (ER)  electromagnetic induction (EMI) EM38 Mapping Field-scale Soil Salinity EMh EMv

6 Approach to Mapping Salinity Use geospatial EC a measurements as a surrogate to characterize soil spatial variability, particularly of soil salinity. Use geospatial EC a measurements as a surrogate to characterize soil spatial variability, particularly of soil salinity. Use spatial EC a information to develop a soil sampling plan that identifies sites reflecting the range and variability of soil salinity and/or other soil properties correlated with EC a. Use spatial EC a information to develop a soil sampling plan that identifies sites reflecting the range and variability of soil salinity and/or other soil properties correlated with EC a. Referred to as “EC a -directed soil sampling” Referred to as “EC a -directed soil sampling”

7 Integrated System: Protocols, Mobile EC a Equipment, and Sample Design Software Perform EC a survey Conduct EC a -directed soil sampling Sample design software Lab analyses & GIS Maps of salinity Identify Sites

8 EC a -directed Soil Sampling Protocols Seven-step protocols*: Seven-step protocols*: ◄ Site description and EC a survey design ◄ EC a data collection with GPS-based EC a equipment ◄ Soil sample design directed by spatial EC a data ◄ Soil core sampling at specified sites ◄ Laboratory analysis of soil physical and chemical properties as defined by project objectives ◄ Spatial statistical analysis to determine the soil properties influencing EC a ◄ GIS database development and graphic display of spatial distribution of soil properties *Corwin, D.L., and S.M. Lesch Characterizing soil spatial variability with apparent soil electrical conductivity: I. Survey protocols. Comput. Electron. Agric. 46(1-3):

9 EC a -directed Soil Sampling Protocols Seven-step protocols*: Seven-step protocols*: ◄ Site description and EC a survey design ◄ EC a data collection with GPS-based EC a equipment ◄ Soil sample design directed by spatial EC a data ◄ Soil core sampling at specified sites ◄ Laboratory analysis of soil physical and chemical properties as defined by project objectives ◄ Spatial statistical analysis to determine the soil properties influencing EC a ◄ GIS database development and graphic display of spatial distribution of soil properties *Corwin, D.L., and S.M. Lesch Characterizing soil spatial variability with apparent soil electrical conductivity: I. Survey protocols. Comput. Electron. Agric. 46(1-3):

10 Conceptual Path Diagram: Factors Influencing EC a Survey of Soil Salinity EC a Survey Target Soil Property: soil salinity Soil property effects: water content, bulk density, temperature, texture Soil condition effects: surface roughness, bed- furrows, etc. Goals: 1.Minimize soil property effects not related to the target property and 2.Avoid confounding influence of soil condition effects Primary Influences Secondary Influences

11 Soil moisture Soil moisture  Ideal moisture condition is field capacity (FC)  General rule: - EC a minimal influence when FC > 70% - EC a substantially influenced when FC < 50% Primary Soil Properties to Consider for an EC a Survey of Salinity Two EMI surveys (7-ha sub-sections) 7 E-W traverses/survey 6 sites/sub-section at 4 depths Soils analyzed: EC e, θ g, SP North South

12 DepthEC e (cm) (dS/m) NS Water content (% of FC) NS SaturationPercentage NS Ave. EC a (dS/m)NorthSouth EMh EMv Soil moisture Soil moisture  Ideal moisture condition is field capacity (FC)  General rule: - EC a minimal influence when FC > 70% - EC a substantially influenced when FC < 50% Primary Soil Properties to Consider for an EC a Survey of Salinity North South

13 Primary Soil Properties to Consider for an EC a Survey of Salinity Soil moisture Soil moisture  Ideal moisture condition is field capacity (FC)  General rule: - EC a minimal influence when FC > 70% - EC a substantially influenced when FC < 50% Soil and ambient temperature Soil and ambient temperature  1.9% increase in EC a per 1ºC increase in soil temperature, which causes temporal effects (e.g., seasonal)  Take soil temperature measurements or conduct survey under same temperature  EM38: protect unit from heat buildup (Robinson et al., 2004, SSSAJ 68: ) < shade the EM38 Texture Texture  Be aware of sharp vertical and horizontal textural discontinuities

14 Secondary Soil Conditions to Consider for an EC a Survey of Salinity Soil surface condition Soil surface condition  Bed-furrows  Surface roughness (e.g., smooth or disked)  Farm equipment traffic patterns (compaction) Metal (e.g., vineyards): concern for EMI units Metal (e.g., vineyards): concern for EMI units Edge effects Edge effects

15 disked flat bed-furrow Meters Bed-Furrow Effect EMh EC a (mS/m) < > 41 N

16 Tractor wheel furrow EC a (dS/m) Furrow Number Effect on EC a Due to High Traffic Compacted Furrows EMh reading

17 What can happen to an EC a survey when factors are ignored? Eleven separate surveys over a 6-month period: Seasonal effects (temperature effects)Seasonal effects (temperature effects) Soil was at other than field capacity (water content effects)Soil was at other than field capacity (water content effects) Soil surface of varying roughness and presence/absence of bed- furrows (surface condition effects)Soil surface of varying roughness and presence/absence of bed- furrows (surface condition effects) EMI Survey

18 Thank You