Fulvic and humic acids are touted as essential in improving soil properties and plant growth. But what exactly are fulvic and humic acids, and do they really have an important role in crop production? Satisfying this question might be easier than explaining the exact mechanism, given the multiple ways that humic and fulvic compounds might interact with each other and fertilizer minerals.
Fulvic and humic acid monikers are used interchangeably, but the truth is, humic acid is a subset of fulvic acid. Fulvic acid comes from lightly digested plant and microbial byproducts and is not just one carbon compound, it’s many varied compounds. Its composition is very similar all over the world, yet it differs slightly depending upon soils, plants, weather, microbes, etc. Fulvic acid, over time, gets degraded, digested and transformed into humic acid which has a denser and tighter carbon structure. These two organic compounds (fulvic and humic acid) contain soil nutrients, ostensibly making soils fertile while improving plant growth and crop yields.
According to the U.S.-based Humic Products Trade Association, the primary use of humates (composed either in-part or primarily of humic substances, humic acids and/or fulvic acids) is to increase plant quality and production, and
to improve and replenish depleted soils.
“Field trials prove that applying humic products helps plants develop much stronger root systems and that length, density and root radius dramatically increase,” states the organization, adding that humic and fulvic acids work together to optimize growing conditions. For instance, humic acids increase the permeability of cell walls, making it easier for fulvic acids to carry nutrients into the plant. And while fulvic acids are the carrier for nutrients, humic acids make those nutrients more readily available in the soil. They also work in tandem to increase water holding capacity and stimulate root and shoot growth.
The application of humic substances is often tank mixed with fungicides or liquid nitrogen when applied to arable crops. Applying them with a mineral fertilizer can be beneficial as the acids prevent immobilization of nutrients and improve uptake by crops, concluded one report by SAC Consulting for the Soil Regenerative Agriculture Group, part of Farming for a Better Climate (FBBC), a network at the Scotland’s Rural College (SRUC) in the UK.
“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,” said Zach Reilly, author of the SAC Consulting report on the FBBC website.
Reilly said another train of thought is that the addition of humic and fulvic acid 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 fertilizer 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 fertilizer did not out-yield the plots with only inorganic fertilizer applied. This raises the question as to whether 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,” said Reilly. “Manures are naturally high in humic compounds and will also assist in increasing soil organic matter content."
There are some studies underway around the world that investigate humic and/or fulvic acids and their effect on cropping systems. Earlier this year, researchers at the University of Alberta in Alberta, Canada, reviewed humic acid relevance on crop growth, plant hormone production, nutrient uptake and assimilation, yield and protein synthesis. The study, ‘Understanding the Role of Humic Acids on Crop Performance and Soil Health’, was published in Frontiers in Agronomy...
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