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?

-97.0889 -97.08885 -97.0888 -97.08875 -97.0887 -97.08865 -97.0886 -97.08855 -97.0885

36.11955

36.1196

36.11965

36.1197

36.11975

36.1198

36.11985

36.1199

1 6

1 8

2 0

2 2

2 4

2 6

2 8

3 0

3 2

3 4

3 6

3 8

4 0

4 2

4 4

4 6

4 8

5 0

5 2

S o i l E C

(6) Nitrogen, Phosphorus, Potash, and Lime 60-30-30+Lime

(5) Nitrogen, Phosphorus, and Potash 60-30-30

(4) Nitrogen and Phosphorus 60-30-0

(3) Phosphorus 0-30-0

(2) Check

(1) Manure every 4 years at 240 lbs N/A

(4) Nitrogen and Phosphorus 60-30-0

Magruder Plots

Lati

tud

e

Longitude

-95.6341 -95.634 -95.6339 -95.6338 -95.6337 -95.6336 -95.6335 -95.6334

35.7408

35.7409

35.741

35.7411

35.7412

35.7413

35.7414

35.7415

-30-20-100102030405060708090100110120130140150160170

Haskell 801150 # 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