The Role Of Humic Acid As A Biostimulant

Humic acid is an important ingredient of any good fertilizer, but many gardeners may not know what it is and where it’s found. Humic acids were first isolated from a German peat bog in 1786, but it's only in recent years that they have been studied. Humic acids are complex organic acids and the most abundant organic molecules on Earth. They occur in sedimentation layers known as Leonardite, which have taken millions of years to form deep in the Earth’s crust. Over time these levels of Leonardite drift upwards until they are close enough to the surface to become oxidised. Mined using simple techniques, Leonardite yields levels of humic acid of up to 70% naturally and once mechanically processed, up to 95%.

What is Humic Acid


 Leonardite is organic plant and animal matter that has become compressed over millions of years. It hasn’t quite reached the state of coal and so is of no use as a fuel. The way that it becomes packed tight together means Leonardite is very rich in humic acids. To understand the cycle, imagine plants growing in a prehistoric peat bog. Insects feed on the plants, then die and fall to the bottom of the bog. Micro-organisms feed on the insects, depositing high concentrations of organic matter. Over time these become compressed into layers. In parallel, plant and animal matter decays to produce humic matter.

 How does Humic Acid work?


Humic acid is full of essential nutrients, trace minerals and vitamins, making it an ideal biostimulant for plant growth. It also has a high oxygen content, which helps increase soil fertility, and it’s not consumed as quickly as compost, peat or manure. Humic acid binds well to soil and is very resistant to microorganisms. Indeed, adding humic acid to soil will increase its mineralization rate. Most benefits are seen in light and sandy soils already deficient in humus.

 What are the benefits of Humic Acid?


Humic acids reduce abiotic (physical) stress in plants caused by excessive salt, drought or temperature extremes. For reasons not yet understood, soils rich in humic acid tend to be well buffered against changes in pH. Keeping soil pH stable is important for nutrient uptake by plants. Stable pH also helps prevent plant uptake of undesirable minerals like aluminium.


The organic matter in your soil is made up of a heterogeneous mix of plant, animal and microbial matter in varying states of decomposition. The biggest and most stable component of soil organic matter is humic acid, which acts by combining with insoluble metals and oxides in the soil. The nutrient compounds formed are released gradually, allowing more efficient take-up by plants. These nutrients also improve the water-holding capability of the soil and help it to crumble, improving aeration. Roots breathe better through increased development. The result is not only up to 70% more yield, but reduced watering and fertilizer use. Increased yields and quality have been observed in many important agronomic crops, such as wheat, rice, maize and soybean. Vegetable crops like tomato, potato, cucumber and pepper have seen similar increases in yield; even some citrus fruits too. Most studies so far have looked at hydroponic methods, with increased root development the most common outcome. But benefits have also been observed in field studies and on plants grown in greenhouses. In one study a preparation of humic acids increased the nitrogen content of wine grapes, and led to a higher tasting score (Morard et al, 2011).

 The Environment and Humic Acid


Using humic acid is kind to the environment too. It encourages root system development, helping reduce nitrates and pesticides entering the groundwater. Humic acid use also avoids the high salt concentrations often found in the soil after fertilizer use. These can lead to NH4 toxicities and excessive root burning.


Unfortunately, humic acids must be replenished on a regular basis to maintain soil fertility. They are removed from soil by wind and water erosion and water leaching. This is why neglecting to top up your soil with humic acid can have a deleterious effect on your crop. Potted plants, small gardens and hydroponic growing need not worry as these stresses are generally controlled.

 Release from Bushboy


Of course, recycling your old crop remains helps to put much needed humic acids back into your soil. Sometimes, though, this isn’t enough; so it’s a good idea to add some extra humic-acid rich plant matter to your soil. Composts and mulches can help, but a simple and more efficient way is to spray humic acid direct on your soil. Bushboy Organics retails a biostimulant called Release, which is 100% soluble humic acid for increased yield. A 1kg pack produces 3,600 litres of solution for use in combination with fertilizer. By mixing the solution yourself, you’re in control how much you need to apply, reducing costly wastage.


It’s small wonder that the use of biostimulants in horticulture, of which humic acid is a major player, is today a multi-billion dollar industry. Most growers agree that growing any crop with humic acid improves crop yield and quality..


References: As supplied by the client









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