Nutrient Solution Formulations

Many nutrient solutions formulations are not specified for use with a particular hydroponic method and/or plant specie. The first 3 formulations, including the Hoagland/Arnon formulations, prepare multi-element concentrates (sometimes referred to as Stock Solutions, usually given a letter designation) that are then combined to form the nutrient solution. Concentrates (Stock Solutions) lend themselves for use with injector pumps that inject a specific quantity of concentrate into a flowing stream of water to form the nutrient solution. This method of nutrient solution formulation is primarily for use with open hydroponic growing systems.

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Major Element Solution No. 1 (without ammonium)
Reagents g/L to use: mL/L
Potassium dihydrogen phosphate (KH2PO4) 136 1.0
Potassium nitrate (KNO3) 101 5.0
Calcium nitrate [Ca(NO3) 2.4H2O] 236 5.0
Magnesium sulfate (MgSO4.7H2O) 246 2.0
Major Element Solution No. 2 (with ammonium)
Reagents
Ammonium dihydrogen phosphate (NH4H2PO4) 115 1.0
Potassium nitrate (KNO3) 101 5.0
Calcium nitrate [Ca(NO3) 2.4H2O] 236 5.0
Magnesium sulfate (MgSO4.7H2O) 246 2.0

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To prepare: weigh the designated amount of reagent into its own 1 liter (L) of water

To prepare the nutrient solution: add the aliquot (mL) designated for each reagent into 1 liter (L) of water to formulate the nutrient solution.
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Micronutrient Stock Solution g/L
Reagents
Boric acid (H3BO3) 2.86
Manganese chloride (MnCl2.4H2O) 1.81
Zinc sulfate (ZnSO4.5H2O) 0.22
Copper sulfate (CuSO4.5H2O) 0.08
Molybdic acid (H2MoO4.H2O) 0.02

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To prepare: weigh all the reagents into 1 liter (L) of water. Add 1 mL concentrated nitric acid (HNO3) and warm to assist in dissolving all the reagents.

Iron

For Solution No.1: 0.5% iron ammonium sulfate [FeSO4(NH4)2SO4.6H2O]; to use: 1 mL/L nutrient solution.

For Solution No.2: 0.5% iron chelate; to use: 2 mL/L nutrient solution

To prepare the nutrient solution: add 1 mL Micronutrient Stock Solution into 1 liter (L) of nutrient solution.

Additional Comments: The author when using these 2 formulations found that the P level is too high, and therefore the aliquot should be 0.5 mL/L rather than 1.0 mL/L for the P-containing reagents. For the Mg-containing reagent, increase the aliquot to 3.0 mL/L from 2 mL/L.

For the Micronutrient Stock Solution, increase the g/L of zinc sulfate (ZnSO4.5H2O) to 0.44 g/L.

To utilize the synergistic effect that ammonium (NH4) has on the root absorption of N as the nitrate (NO3-) anion, add one teaspoon of either ammonium nitrate (NH4NO3) or ammonium sulfate [(NH4) 2SO4] to the potassium nitrate (KNO3) reagent in the Major Element Solution No. 1 formulation.

Dilution for use with the sub-irrigation hydroponic method: add each of the designated mL of the Major Element Stock Solution No. 1 (without ammonium) and the Micronutrient Stock Solution into 1 gallon of water.
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In this formulation, all of the reagents are dissolved in 1,000 L of water to form a complete nutrient solution. The procedure can be cumbersome when large volumes of nutrient solution are needed.

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Theoretically Ideal General Purpose Complete
Nutrient Solution
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Reagents  g/1,000 L
 Calcium nitrate [Ca(NO3) 2.4H2O] 1,003
 Magnesium sulfate (MgSO4.7H2O) 513
 Potassium dihydrogen phosphate (KH2PO4) 263
Potassium nitrate (KNO3) 583
Boric acid (H3BO3) 1.70
Copper sulfate (CuSO4.5H2O) 0.39
Manganese sulfate (MnSO4.4H2O) 6.10
Ammonium molybdate [(NH4) 6Mo7O24.4H2O)] 0.37
Zinc sulfate (ZnSO4.7H2O) 0.30

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There are circumstances when formulating a nutrient solution that one or only several of the major elements are needed. Stock solutions containing one or 2 of the major elements: N, P, K, Ca, Mg and S, can be useful when formulating a nutrient solution when a particular elemental content/concentration is required, or for reconstituting a nutrient solution that is to be re-circulated when only one element or a group of elements are needed.

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General Purpose Major Element Stock Solutions

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Major Element Stock Solutions
Reagents g/L to use: mL/L
Calcium nitrate [Ca(NO3) 2.4H2O] 787 1.25
Magnesium sulfate (MgSO4.7H2O) 329 1.5
Potassium dihydrogen phosphate (KH2PO4) 91 3.0
Potassium nitrate (KNO3) 169 3.9

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To prepare: dissolve each reagent in its own 1 L of water.

To prepare the nutrient solution: add the designated to use aliquot to 1 L of water.

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A micronutrient formulation for general purpose use can be useful when formulating a nutrient solution, or when reconstituting a nutrient solution that is to be re-circulated by only adding the micronutrients that have been depleted.

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General Purpose Micronutrient Stock Solution
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Micronutrient Stock Solution
Reagents g/L
Boric acid (H3BO3) 1.23
Copper sulfate (CuSO4.5H2O) 0.17
Manganese sulfate (MnSO4.4H2O) 1.50
Ammonium molybdate [(NH4)6Mo7O24.4H2O)] 0.06
Zinc sulfate (ZnSO4.7H2O) 0.38

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To prepare: dissolve all the reagents in 1 liter (L) of water

To use: add 1 mL of the prepared Micronutrient Stock Solution to 1 liter (L) of a major element nutrient solution, or to a nutrient solution that is to be re-circulated to restore its the micronutrient concentration.
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Specialized Nutrient Solution Formulations

Some nutrient solution formulations have general use applications that only contain the micronutrients, or they have specialized use based on the balance among the elemental constituents.
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Arnon’s Micronutrient Formula

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Reagents mg/L
Boric acid (H3BO3) 0.48
Copper sulfate (CuSO4.5H2O) 0.008
Manganese sulfate (MnSO4.H2O) 0.25
Zinc sulfate (ZnSO4.7H2O) 0.035
Molybdic acid (MoO3.2H2O) 0.1104

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To prepare: dissolve all reagents in 1 liter (L) of nutrient solution.
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Solid Matrix Formulation

There is significant advantage in having the reagents in solid form for making a nutrient solution so that only a weight or volume measurement is sufficient to make a nutrient solution.

Reagent A
Calcium nitrate [Ca(NO3) 2.4H2O]
Reagent Mix B grams ounces
Potassium nitrate (KNO3) 2,275 80.25
Magnesium sulfate (MgSO4.7H2O) 1,757 62.00
Potassium dihydrogen phosphate (KH2PO4) 878 31.00
Boric acid (H3BO3) 6.0 0.200
Copper sulfate (CuSO4.5H2O) 2.0 0.075
Zinc sulfate (ZnSO4.7H2O) 1.5 0.053
Ammonium molybdate [(NH4)6Mo7O24.4H2O] 0.35 0.0125
Iron EDTA 132.0 4.65

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Preparation of Reagent Mix B: blend all the reagents together and thoroughly mix. The granular size of each reagent should be the same to ensure a homogenous mix.

To prepare the nutrient solution: to 10 liters (2.65 gallons) of water, add 1 level teaspoon of Reagent A, stir until dissolved, and then add 1 level teaspoon of Reagent Mix B and stir to dissolve.

Comment: The reagents must be of uniform particle size. To prepare a homogenous Reagent Mix B is not an easy task so that each teaspoon aliquot contains the weight proportion of each reagent. In addition, the mix must be stored in a moisture-free atmosphere to prevent water adsorption.