Sometimes humic acids substances are added to heavy metal contaminated soil for remediation purposes because of their ability to form stable complex with metals.

Appreciable quantities of humic acids are too expensive for most purposes

Tamjid Us Sakib is correct that humic.fulvic acids are able to help ameliorate issues of toxicity and help in soil remediation from heavy metal contamination.

Humic acids are heterogenous diverse compounds which have 10,000 to 100,000 mol weight and are usually extracted in potassium hydroxide solution.

Humic acids can work as chelators not only does this reduce toxicity as in the case of heavy metals but the chelation can improve the movement and absorption of immobile elements such as iron and phosphrous.

The concentration of a few to a few hundred ppm of humic acids are stimulatory to seed germination.

The activity is related to increasing the respiration and defensive reactions but the humic acid is also a notable ability to serve as an antioxidant.

In addition to respiration and defensive stimulation the humic acid supplementation is found to increase chlorophyll content and photosynthesis.

For animals the inclusion of humic acid in animal rations has been shown to reduce to viral digestive issues and improve feed conversion.

Humic acid has proven ability to act as growth regulator and the humic acid can greatly stimulate both rooting and drought reactions. Rooting effects is to stimulate the rapid initiation of root initials and branching.

Humic acids also work as buffering agent for soil pH reactions.

Humic acids are known to stimulate beneficial soil microbes helping to establish symbiotic organisms such as Rhizobia and mycorrhizal fungi.

Because of the low dosages needed from growth responses the humic acids can be used as cost effect crop stimulants.

The presence of organic matters are well documented to be associated with highly productive soils and their accumulation can help counteract atmospheric greenhouse gases.

Humic acids are effective at parts per million concentrations. The Compost of manures and the production of vermicompost yield humic acids which can be extracted in teas to yield the stimulating extracts. For home use 3 handfuls put into 20 liter pail filled with 3 quarters of water and stirred gives an effective compost tea which has good concentration of humic acids. The compost tea can be used foliar application strained solids as plant mulch. The compost tea can used as drench also. These preparations give good effects without any need to have a high cost.

Thanks Paul for good information

Is humic acid is better for maintenance of soil pH from alkaline to neutral?

When Paul Milham suggests humic acids are expensive he may be referring to the cost of prepared products. In terms of economics the advantage of the product is it action is due to growth regulating properties effective at just low numbers of parts per million. As such depending on the response and the value of the products produced economics can be highly favorable but need to be determined by efficacy and economic analysis. This ability should not be discounted out of hand without testing and calcuations.

Humic acid substances increase availability of nutrients particularly micro-nutrients, also, improve plant growth under stress conditions like salinity

There is a query if humic materials are better in alkaline or acid conditions??

. I believe that in the alkaline condition the humic materials help to resolve issue such as carbonate mediated inavailability of micronutrients this is supported by Waleed Abobatta observations. in saline and alkaline environments.

Many times in my own experience an iron chlorosis is greatly aided by humic materials. Rarely is iron ever truly deficient but usually just inavailable based on the soil condition.

In terms of acid environments the issue is both deficiencies and toxicities in acid soil toxicity.

Humic material is very effective in helping but acid soil toxicity such as iron, aluminum and manganese and to aid in mobilizing deficiency elements. In my experience humic materials are useful for a broad scope of soil and plant nutrition issues. In their ability to help address both toxicities and deficiencies they are somewhat unique.

The final mechanisms which should be considered is the information that humic materials as growth regulating substances stimulate the plant defensive mechanisms in a broad sense at low concentrations.

The use of humic materials is also been shown to have significant anti viral and microbial effects. The humic materials also are substrates for native probiotic soil and plant floras.