Soil Electrical Conductivity: Functions and Uses for Precision Agriculture

What is Soil Electrical Conductivity? measure of voltage drop from one electrode to another (Veris) – physical contact needed electromagnetic induction (EM) uses electromagnetic fields to measure EC – no physical contact needed (EM38) simply how fast the current moves through the soil pores pumps out a GPS referenced number – “apparent” EC in milliSiemens (mS) per meter (EM38) or “bulk soil” EC also in mS per meter (Veris with DGPS)

EM38 Veris 3100

What Affects Soil EC? Several soil properties Pore space (clay v. sand) continuity Current water status Salinity (concentration of salts in the soil water) CEC (the higher the CEC, the more ability to retain positive ions on the exchange sites – touted to “enhance” soil EC much like salts do) Depth of measurement – signal strength is gets weaker the deeper you measure

What Affects Soil EC? (still) Temperature – EC decreases slightly with colder soils Organic matter Clay content

Nice map, huh? Magruder Plots Latitude Longitude

Haskell 801 150 # N/A/yr

More nice maps Soil Conductivity in relation to a soil map Yield and Conductivity

What is it used for? Not necessarily a measure of productivity Make the map, watch the patterns

Really, What is it used for? Maps are used to identify problematic areas Soil EC patterns are stable over time If the EC data (converted to maps) is correlated with those factors mentioned before, EC is used as a substitute soil test of sorts – indirect measurement Factors that are known to influence yield (water holding capacity, for instance) could help to make management decisions such as seeding rates, nitrogen fertilization rates, etc.

Who uses this? University of Missouri (Kitchen, Sudduth) “…We have used these techniques in combination with soil EC sensors and GPS-derived digital terrain maps to allow us to map soil differences within fields. For example in the figure in red we show an Order 1 soil map from one of the Illinois fields over a Veris soil EC map. It is clear that there is very good agreement between the two maps. Through our research, we have found that the Veris EC data are more useful in describing yield than the Order 1 soil map. When predicting the yield from a given section of a field, a combination of soil EC, past yield, terrain, and soil fertility can explain in excess of 80% of the yield variability. It is also important to note that a Veris EC map can be made in less than a day, while the production of an Order 1 soil map takes many hundred man hours.”

Who uses this? KSU “…focused on correlating EC values with such important soil parameters as texture [especially clay content], organic matter, salt content, moisture, and fertility across a wide variation in geologic and climatic conditions. For example, some studies show that the sand, silt, and clay fractions of soil tend to have low, medium, and high EC, respectively.”

Who uses this?(other than Universities) Several Consulting Companies $4.00/A, $3.50/A (them), $1.50/A (you-pull-it) HGCA