Nutrient Soultion for Testing Symbiotic Nitrogen–Fixing Bacteria

Courtesy Nitragin Sales Corp.

Milwaukee, Wisconsin

Founded 1896

Symbiotic Nitrogen-Fixing Bacteria   feed on the roots of some plants.

However, they also breath-in Nitrogen from the atmosphere and convert it to Ammonia, NH4. Another group of bacteria then feed on the Ammonia and convert it to a Nitrate, NO3. Plants Need to find their Nitrogen as NO3. It has to do with Electricity.

These Rhizobia Bacteria, capture from the atmosphere each year for commercial farmers, Billions of dollars of Nitrogen Fertilizer, saving oil, which is another source of Nitrogen Fertilizer.

Take a Slide Show Tour of the Factory

Testing Nitrogen Fixing Rhizobia Bacteria 
Click on picture to see enlargement. Normally in measuring the nitrogen–fixing abilities of rhizobia, it is desirable to grow the host plant in a nitrogen–free medium. Several nitrogen–free nutrient solutions are in common use and perhaps each has its advantages and disadvantages.

Nitrogen Fixing Rhizobia Bacteria Nodules on Peanut plant roots. 
Click on picture to see enlargement.

The important point is that the host plant be well nourished but not overly nourished with all nutrients needed for growth except nitrogen and the various elements should be in balance for the specific host.

Nitrogen Fixing Rhizobia Bacteria Nodules on plant roots. 
Click on picture to see enlargement. Since nutrient requirements of plants vary with the species and with environmental factors, it is unlikely that the perfectly balanced medium can often be obtained. Bryan's modification of Crone's salt formulation (Soil Sci. 13:279) appears to be the most commonly used and has generally worked out satisfactorily. It is usually supplemented with micronutrients.

The Nitragin modification is given below:

Nutrient Salt Formulation

Mineral Salt Chemical Formula grams / l. ppm. ( final )
Potassium Chloride KCl 10.0 g. 393.3 ppm. K
Calcium Sulfate CaSO4 • 2(H2O) 2.5 g. 116.3 ppm. Ca
Magnesium Sulphate MgSO4 • 7(H2O) 2.5 g. 18.5 ppm. Mg
Tricalcium Phosphate Ca3(PO4)2 2.5 g. 80.2 ppm. P
Ferric Phosphate soluble
2.5 g. 26.2 ppm. Fe

      pH of nutrient solution (100 ml. 4 Normal H2SO4) = 2.00

      pH of sand moistened with above solution and autoclaved ranges from 7.6 to 8.2.

  • Mix all salts and grind to a fine powder with a mortar and pestle.
  • Add 1.5 g. of the salt mixture to one liter of distilled water.
  • Supplement with Micronutrient solution and iron as indicated below.
  • Presently 100 ml. of 4 Normal of H2SO4 added to 9 liters of nutrient solution brings about the desired pH with sand alone.
  • When "Terra–Lite" is used in the glass jars, only 50 ml of 4 Normal H2SO4 is needed.

Micro–nutrient Stock Solution

Mineral Salt Formula grams / l. ppm. (final)
Boric Acid H3BO3 0.57 0.50 B
Manganese Sulfate MnSO4 • H2O 0.31 0.50 Mn
Zinc Sulfate ZnSO4 • 7(H2O) 0.09 0.10 Zn
Copper Sulfate CuSO4 • 5(H2O) 0.08 0.08 Cu
Molybdic Acid (85% MoO3) 0.016 0.04 Mo
Cobalt Chloride CoCl2 • 6(H2O) 0.0008 0.001 Co

Micronutrient stock solution should be added at the rate of 5 ml. per liter or 45 ml. per 9 liters of nutrient solution.


The modified Crone's solution with soluble ferric phosphate contains iron citrate which is a chelated form. No additional iron is needed unless the pH of the nutrient solution is above 6.8

(The rest of this discussion is hiding in my archives somewhere and will be posted as soon as I find it.)

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