If this is your first stint at gardening, you're probably new to such terms as slow release fertilizer, soil organic matter (SOM), humic substances, etc. Nonetheless, you must have come across the term humus in science classes as a kid. Allow me to prod your memory a little more. Remember having read something about dead plant matter that stays mixed in soil being good for plant growth? Ah! I saw that flash of recollection cross your eyes! Well, humic substances are nothing but organic matter in the soil that is still undergoing decaying processes. Once the decay is complete and the organic matter cannot be broken down further, we get what we know as humus. In other words, we get humus when humic matter reach the last stage of decay beyond which it cannot decay further.
So, what is humic acid then? Well, humic acid is a chemical component which is composed of many other chemical components and is a major constituent of humic substances. The composition of humic acid is quite complex as it is made up of various different acids belonging primarily to phenolate and carboxyl groups. Apart from their conventional use as plant nutrition supplements and added to soil, recent research has shown that humic acid and fulvic acids have huge benefit for human nutrition and immunity owing to their rich organic content and antiviral properties. That being said, let's proceed forward to the next segment and find out how to make humic acid at home.
Steps to Make Humic Acid Yourself
You can either extract humic acid from a humus rich soil sample, from peat moss or from humic compost. If you regularly add humic compost to your garden then sourcing humic acid from both humus laden soil or the organic compost would be easy, though quite tedious. Extracting humic acid from peat or peat bogs can be even more taxing if neither are available within close vicinity of your garden.
Anyway, let's go along the relatively simpler, but equally time-consuming route and find out how humic acid can be extracted from garden soil to which humic compost is added on a regular basis.
- Take as ample soil sample as a lot of soil, say five cups, will produce only a little bit of humic acid, say half one cup. Remove all roots and bits of grass or leaves from the soil sample by sieving it.
- Add 1 M hydrochloric acid to the soil sample so that its pH value comes somewhere between 1 - 2 on a pH scale when kept in room temperature.
- Add some more hydrochloric acid to the solution so that the solid:liquid ration stands at 1g:10 ml. Shake the container containing this solution for about an hour or so and then set it down to allow the solid particles to settle to the bottom of the container as the residue.
- Slowly and carefully, pour out the liquid into another container, taking care not to unsettle the solid residue at the bottom of the container. This way, the supernatant liquid gets separated from the solid soil residue.
- Add 1 M of sodium chloride to the soil residue to achieve a pH reading of 7, which means that the pH of the residue is neutral. Add some more sodium chloride to the residue so that the ratio between sodium chloride and the residue becomes 10:1. The additional sodium chloride should be introduced to the residue in the presence of nitrogen.
- Keep the suspension for about 4 hours, shaking it in regular intervals. Let the suspension stand for the entire night and in the morning, separate the supernatant and the residue by pouring the supernatant out into another container as mentioned above.
- Add some hydrochloric acid to the supernatant till the pH value of this solvent mixture is 1.0. Keep stirring constantly as you mix the two.
- Let this suspension stand for about 14 hours and then separate the resultant powdered humic acid (precipitate) from the fulvic acid via centrifugation as decantation is no longer possible.
- In the presence of nitrogen, mix the humic acid precipitate with 1 M of potassium hydroxide and add enough potassium chloride to attain a concentration measuring about 0.3 M. Separate the precipitates by centrifugation and add 6 M of hydrochloric acid to again form a humic acid precipitate with a pH of 1.0. Keep stirring constantly all along.
- Let the mixture stand for another 14 hours and thereafter separate the residue from the supernatant by centrifugation.
- Add the humic acid powder in a hydrochloric acid and hydrofluoric acid solution in a ratio of 0.1 M:0.3 M in a plastic vessel. Shake the container for about 8 - 10 hours in room temperature.
- Separate by centrifugation and repeat the previous step till the ash content of the mixture goes down to 1% or less.
- Shift the humic acid precipitate to a dialysis tube, add some water to form a muddy mixture and allow the mixture to undergo dialysis in opposition to water that has been distilled.
- Keep dialyzing till the water in which dialysis takes place shows a negative reading when tested with silver nitrate.
- Dry the humic acid by keeping it in a frozen environment.
- Now, take the supernatant saved from the first solution of soil and hydrochloric acid and pass it through a column of absorbent resin.
- Clean the resin column by getting rid of the effluent and back elute with 1 column volume of 0.1 M sodium hydroxide and 3 columns volumes of distilled water.
- Add hydrochloric acid to the solution so that its pH becomes 1.0. Add 0.3 M of concentrated hydrofluoric acid to this solution, taking care to retain the fulvic acid content of the solution.
- Repeat this process with the supernatant left over after separating humic acid precipitate from fulvic acid earlier in the process. Mix the resultant elutes from this and the previous step and pass this final product through a column of absorbent resin to collect it in a glass column. Clean the resin column with distilled water and conduct back elution as instructed before (by adding 1 column volume of 0.1 M sodium hydroxide and 2 column volumes of distilled water).
- Filter the final elute using a hydron soaked cation swapping resin. Freeze dry.
Whew! That's how you make humic acid! Neither very simple nor time efficient, I would say. Therefore, unless you have plenty of time on your hands and the proper laboratory equipment at your disposal, don't bother going through all this trouble. If soil additive is what you want, just dig a hole in an obscure corner of your garden and put in shredded vegetable matter, adding just enough moisture now and then, to get home-made, organic compost rich in humic substances. For health and nutrition purposes, you would be better off getting ready-made humic acid pills from your local chemist or ordering them on the Internet.