Dan Kittredge: 4 methods to measure nutrient levels in your soil

by Franziska Matt & Andrew Toth
Dan Kittredge is an expert for nutritious soils, plants and crops.
His “principles of nutrient density” revolutionized the way farmers approach their work. It is an entire paradigm shift.

The idea tracks back to the very origin of the supply chain, namely the natural environment. Right there, an optimal nutrient supply has to be guaranteed so that benefits can be enjoyed by both farmers and consumers. But how can farmers determine the nutrient quality in their soils?

Hands in the Soil

A prevalence of the following chemical elements can be considered as first indicators:

  • copper

  • iron

  • zinc

  • manganese

  • boron

  • sulphur

Measuring method 1:

testing the soil’s electrical conductivity

The USDA defines electrical conductivity (EC) simply as a measure of the salts in your soil. Drawing that out a bit: electrical conductivity is a measure of a soil’s ability to allow electrons to flow through it (i.e. conduct an electrical charge.

Conductivity in soils relates most importantly to two things:


  • Quantity of nutrients

  • Mobility of ions (cations & anions)


Generally, a high EC value indicates presence of negative charges (such as organic matter!). These negative charges have positive counterparts which also tend to be good: sodium, ammonium, potassium, calcium, magnesium, and manganese, to name just a few.


That being said, you don’t want EC to be too high either, as too much of a good thing can be a bad thing. EC of soil is typically measured in milliSiemens per centimeter (mS/cm).


Specific EC targets vary depending on what you are growing, but you can assume the EC should be somewhere between 1 and 6 mS/cm.

soil test.png

A simple electrical conductivity probe can be used to quickly test your soil’s conductivity. The probe shown here costs about $120 (image courtesy of www.soilworksllc.com).

>> Substances to enhance the soil’s natural EC

  • seaweeds

  • soil vaccines

  • humates (salts which have some of their protons substituted by cations, e.g. calcium or iron humates)

  • finely-ground minerals or sediments

“On the one hand, a ‘free-flowing’ soil means that energy can be measured optimally at any time. On the other hand, it indicates that the ideal circumstances for biological growth are given.”

– Dan Kittredge

Measuring method 2: refractometer

Refractometers can identify dissolved substances in liquids.


In the context of the topic at hand, a refractometer measures refractive light that passes through plant sap or fruit/vegetable juice to measure nutrient levels.


The refractometer’s unit of measurement is a “brix”. Responding to complex carbohydrates, complex proteins and non-reducing sugars, this method shines further light on the quality of a soil.


Nutrients featuring a high proportion of brix come with several advantages: many vitamins and minerals, superior tasting products, and longer shelf life of produce.

Measuring method 3: Phil Callahan Soil Meter (PCSM)


Here is an example of an analog refractometer (digital devices are much more common on the market today and cost $50-$150, but this picture is more fun than the pictures of digital refractometers). Based on this man‘s smile, you can see it’s mighty enjoyable to use a refractometer (image courtesy of ecofarmingdailycom)


Here’s example of a PCSM. A soil sample goes into the port in the lower lefthand side of the device. The cost for this beautiful device is $575. (Image courtesy of pikeagri.com)

The PCSM is used to determine the paramagnetism of a soil. Paramagnetism refers to the magnetic susceptibility of atoms or molecules to be influenced by an applied electromagnetic field (paramagnetism is measured in millionths of centimeters Grams Second, or µCGS).


The greater the measured value, the higher the plants’ abundance of nutrients.

Worth considering: A paramagnetic measurement below 200 µCGS  means there is an energy deficiency. Such conditions impede chemical reactions and prevent optimal plant growth. Values between 200 and 600 µCGS in the soil are ideal, whereas values over 1,000 µCGS are counterproductive.


In the plant, values around 2,000 µCGS and above are desirable.

Measuring method 4: pH-value

This value clarifies the relation of hydrogen ions (H+) and hydroxide ions (OH). A very simple digital soil pH meter costs under $30.

Worth considering: Water usually has a pH of around 6. For optimal growth, plants prefer a pH-value of 6.4. Everything above 6.4 implies a deficiency of anions (i.e. insufficient nitrogen, phosphate and sulphur). Insect attacks are most likely to happen at a pH level above 8!

A pH-value below 6.4 comes with a deficiency of cations, which can be recognized as insufficient calcium, magnesium, potassium and/or sodium. An undesirable consequence in such an environment can be leaf diseases. Also interesting: a pH-value below 4.5 causes fungal attacks!

Worth considering: An energy deficiency in the soil leads to plants being unable to metabolize minerals and this keeps the plant’s fruit from thriving. For practical methods to strengthen the energy flow, see “Dan Kittredge: principles of nutrient density”. 


“I’m gonna measure the pH

Only got twenty dollars in my pocket

I’m, I’m, I’m hunting,

looking for a meter

This one is in stock (here)”

(Image courtesy of plantcaretools.com)