Soil Electrical Conductivity Measurement and AgOpenGPS

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Wondering if anyone has done any work building a DYI “on-the-go” electrical connectivity tester and interfacing it with AgOpenGPS?

Soil’s electrical conductivity is related to soil ph and fertility. My field was land-leveled and its clear from the difference in coloration of the soil and crop performance that my soil health varies through out the field (top soil stripped off some spots and deposited in lower spots).

So I need to come up with a plan to apply fertilizer at different rates through out the field to start to balance the soil productivity in my field.

Based on a bunch of reading, the best way to do this is buy or build an “on-the-go” electrical conductivity tester, drive it around the field logging conductivity including lat/long of each reading and then build some vector files that can be loaded into agIO and used when applying fertilizer.

The way to build an “on-the-go” tester is to essential:

  1. put six coulters on a 3-point tool bar electrifying two coulters and then read the resulting voltage based on the distance and depth of the other four coulters (Development of a soil electrical conductivity measurement system in paddy fields | Ho | International Journal of Advances in Applied Sciences)

  2. Reading the voltage drop through the soil is similar to using an Ohm meter. The variation in voltage indicates variation in soil health. The key is to build a logger so each reading can be matched paired with GPS position. (https://cdn.prod.website-files.com/663a7ed036a46c8036913b96/66752d3671abf0fc27676ca9_Ohm_On_The_Go_Project_Documentation_compressed.pdf)

  3. Use AgOpenGPS to log the lat/long position of where each reading is taken.

My plan is to join the output file of AgOpenGPS NMEA’s reading with the ohm meter logger after the field has been transited. The challenge to this is that the current output from AGOpenGPS seems to only record lat/long. Any suggestions on how to modify the output language to include time and elevation (time so I can join the two log files based on time and elevation because I hope to use OpenGrade this spring to reduce the slope of some remaining unevenness in my field)?

The analysis that needs done in GIS once I have recorded resistance values over the field is to:

  1. load the results as point file in QGIS,
  2. convert points to raster,
  3. merge pixels with similar value,
  4. create a vector boundary files for areas with similar conductivity readings.

Once this analysis is done, the next step is to
a) take samples of the soil in the different areas and have them tested at a lab,
b) work with a fertilizer distributor to come up with a fertilizer plan and
c) then put the vector boundaries into agIO so I can apply fertilizer at different rates to the different areas according to need. (Likely calculate a base rate of application for setting fertilizer cart doors, and then make the correct number of passes over each part of the field turning off the PTO similar to section control until I correctly apply fertilizer to each area in the field.)

My questions are:

  1. has this been done before and I am missing the discussion in my searches?
  2. Any guidance on adding time and elevation to agIO’s output file?

Many thanks for any help.

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