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Humic and Fulvic Acid

Humic and fulvic acids are often considered necessary additions to the sprayer tank in many regenerative systems, however at approximately £3/litre and often applied several times throughout the season, the cost can add up quickly.

The Soil Regenerative Agriculture Group have been questioning how they work and if are they worth it?

Humic and Fulvic acids are complex acids which are found in humic substances in the organic fraction of the soil. When plants and animals are decomposed by bacteria, these acids are released and are naturally found in soils and water courses. In agricultural systems, they are believed to aid nutrient uptake as the acids can bind with minerals, a process known as chelation, and then allow the minerals to be taken up by the plant.

Humic and fulvic acids have been found to promote plant height and root density when applied in low doses. Although there is much research on the effect of these acids on seedling growth, little work has been done to monitor their effects on yield differences in cereal crops. Seedling root growth and germination in a variety of crops are well-documented benefits of applying these acids and are perhaps the main drivers for there use in regenerative systems. The absence of tillage can create a challenging environment for seedling growth if the soil is hard, and the application of humic and fulvic acid may go some way to combatting this challenge. However, the research finding these benefits are a consequence of using a seed coating application prior to sowing, whereas humic substances are often found in the spray tank later in the season in practice. This raises the question as to why they are being applied to an established crop.

The application of these substances is often tank mixed with fungicides or liquid nitrogen when applied to arable crops. Applying them with a mineral fertiliser can be beneficial as the acids prevent immobilisation of nutrients and improved uptake by crops. Common practice is to apply 2-5l/ha in each spray application, depending on the product chosen. However, research points to the biggest gains arising from an increase in the availability of phosphorus, and when the acids are mixed in with the fungicide sprays, most if not all the phosphorus is likely to have been applied already. Furthermore, the addition of these humic substances alongside nitrogen, a highly mobile nutrient, has not been found to increase yield. Again, raising the question as to why these products are commonly used?

Another train of thought is that the addition of humic and fulvic acid, or the use of molasses can reduce the impact a fungicide or nitrogen application can have on the soil biology. This is thought to be achieved by providing a carbon source to provide energy to the microbiology to combat the effects of the mineral fertiliser or pesticide. Although this is a promising theory, there is very little research on its effectiveness.

Scottish specific research on ryegrass found that the application of humic and inorganic fertiliser did not out-yield the plots with only inorganic fertiliser applied. This raises the question if humic acid is worthwhile. If the soil is healthy with optimal organic matter levels, do these naturally occurring compounds need to be applied?

If soil is in an unhealthy state, the addition of bulky manures may be a more suitable soil addition, either by integrating livestock or as an application. Manures are naturally high in humic compounds and will also assist in increasing soil organic matter content. If you want to try it at home, hold your own split field trials, investigating the effects the additional humic and fulvic acid can have if applied as a seed or foliar treatment. Furthermore, a comparison against the application of an organic manure such as cattle dung would make an interesting experiment if taken through to yield.

Zach Reilly, SAC Consulting

Read more about the Soil Regenerative Agriculture Group.