Humic and fulvic acids and their benefits
By Patrick Regnault
Humic and fulvic acids are used as bio-stimulants to promote plant growth and increase nutrient availability and uptake. The ornamental horticulture industry is looking to reduce its environmental impact – think of all the fertilisers used on lawns and gardens, sport fields and parklands. Bio-stimulants have a place in reducing environmental damages. Humic and fulvic acids are non-microbial bio-stimulants.
Humic acids are high-molecular weight compounds that are soluble at alkaline conditions, whereas fulvic acids are comparably lower molecular weight compounds that are soluble at both acidic and alkaline conditions. (1) (2)
Fulvic acids are small in size making them easier to be absorbed by plants and facilitating the uptake of minerals and nutrients into plants, thus improving plant growth.
Humic acids improve soil characteristics by increasing soil porosity, water holding and cation exchange capacities. They also promote plant growth by improving nutrient use efficiency and abiotic stress tolerance. They have a positive impact on root development which improves drought resistance and nutrient intake, resulting in improved shoot growth, chlorophyll content and photosynthesis, and increased flower number and fruit size which is useful in the home orchard and the vegetable patch. Humic acids have been shown to help repair contaminated soils by fixing heavy metals and degrading organic pollutants.
In a site with disturbed soils, treating the soil with a combination of fulvic acid, humic acids and calcium can greatly improve a plant’s ability to establish. Spraying humic and fulvic acids on lawn will help encourage a deeper root system, unless the soil has not been prepared correctly and is very compacted.
Those non-microbial bio-stimulants can be used as a foliar spray and a soil spray. They can also be used, and sometimes sold, in combination with microbial bio-stimulants. Those combinations are very efficient to help highly disturbed soils such as cut and fill.
Humic and fulvic acids come in granular and liquid forms, and also in a combination with fish and seaweed. The rate of spray will vary depending on if it is for soil improvement, turf, ornamentals, orchards or vegetables. For soil improvement, the rate will need to be on the highest range to be effective. Follow the indicated rate as it may vary depending on the brand.
It is important to remember that the effect of most bio-stimulants will be better seen when plants are under abiotic stress conditions. Personally, I do use bio-stimulants for disturbed soils and when I am called upon to solve an existing problem with a garden that is not thriving, the result being a rapid improvement in plant and soil health. I also use it prior to laying turf as it seems to help with faster turf establishment.
There is an environmental impact in the making of those acids. There is no free lunch; everything is a cost to the environment. The main sources of humic and fulvic acids are either from Leonardite or from peat bogs. Leonardite is usually found in the upper layers of open coal mines, and this has well-known environmental costs. The acids are then extracted from the mineraloid by various processes, some less damaging than others. The peat bog extraction is deemed more sustainable, mostly by those extracting it. It can be done with minimum damage to peat bogs, mostly in countries with strong environmental regulations and only if those are adhered to and properly checked by unbiased and non-corrupted protection authorities – a big ask in my view.
The environmental cost benefit is not an easy one. I could not find a clear answer that may help you in your decision. Chemical fertilisers may have to be phased out in the medium to long term. Humic and fulvic acids can be manufactured using waste from tanneries and organic matters, but this also comes at a cost.
References:
1. Calvo et al., 2014, Agricultural uses of plant biostimulants.
2. Stevenson, F.J., 1994, Humus Chemistry. Genesis, Composition, Reactions.
Patrick Regnault FAIH RH0062
Interactive Landscapes
E: patrickregnault@hotmail.com