By Russell Taylor, CCA, Live Earth Products
With growers’ renewed focus on improving soil health, old products like humic acids are getting a fresh look in the specialty crop market. Humic acids are a vital component of soil health, and when isolated into concentrated liquids, they also play an important role in addressing nutrient management and salinity issues. Humic acids are a tool for all growers.
What are humic acids?
Humic acids are a complex mixture of organic acids derived from the decomposition of organic matter. Although found in all soils in trace amounts, they are often ignored as the foundational component of soil organic matter. Compost, manure, and soil microbiology break down into stable macromolecules that form soil humus, but it takes a lot of degraded material to form humic acids. Most commercial sources of humic acids are extracted from ancient plant deposits like degraded peat bogs, leonardite, or humic shale. Humic acids play a significant role in soil structure, nutrient cycling, and salt mitigation. More importantly, some observed benefits of humic acids mixed with plant nutrients in foliar applications, as discussed in detail later, are ancillary to soil health.
Why include humic acids in fertility plans?
Humic acids enhance nutrient availability by making essential plant nutrients more accessible for growth. Research shows increased nutrient availability with the application of humic acids (Yang et al., 2021), but the process of how it does this is still being studied by researchers.
For example, nutrients like calcium and phosphorus sometimes react with each other in ways that make them less available to plants. Humic acids have many nutrient exchange sites, often described as cation exchange capacity (CEC). Adding humic acids can prime those nutrients to help delay those negative interactions that reduce nutrient availability.
Think of it like adding more chairs to a game of musical chairs — with more chairs available, more nutrients have a place to “sit” and stay accessible to plants. When fertilizers dissolve, they break down into ions such as potassium, calcium, magnesium, ammonium, and micronutrients like iron, manganese, and zinc. These positively charged nutrients interact well with humic acids, which helps protect them from adverse reactions that can reduce their availability (similar to how chelates work). Blending nutrients with humic acids before application can reduce nutrient tie-up and loss.
Humic acid’s cation buffering benefits
Humic acids are commonly blended with agricultural nutrients to improve nutrient availability to the plant. In addition to fertility management, the high CEC of humic acid is beneficial as a buffer in situations where excess cations in the soil or fertilizer cause unfavorable environmental conditions for the plant.
Cation buffering is especially useful in soils or applied water with excess nutrients or salinity. Most humic acid buffering research is done in soil mediums as an amendment. One recent trial indicated the benefit of increasing the tolerance mechanisms of salt-sensitive strawberry plants (Dikilitaş, et al., 2021).
Similar results were previously observed on strawberry plants treated with humic acids, which were able to compensate for the harmful effects of salinity (Saidimoradi et al., 2019).
Other trials illustrate the benefit of humic acids treating water and foliar sprays. One study found that humic acids buffer calcium in a spray solution, which is beneficial in mitigating the adverse effects of calcareous conditions (Hakan et al., 2010). The benefit of foliar-applied humic acids positively impacted nutrient utilization by the plant and was independent of the nutrient content of the humic acids.
Research also indicates that in addition to calcium, other cations, like sodium, are similarly buffered by humic acids in fertilizer sprays and irrigation water. In another study, humic acids applied as a foliar spray effectively reduced the leaf sodium concentration while improving the accumulation of plant nutrients nitrogen, phosphorous, calcium, and potassium (Kaya et al., 2018).
Humic acids also interact positively with foliar-applied nitrogen fertilizers, specifically ammonium (Osman et al., 2013). While this study demonstrates that using humic acids with fertilizer increases grain nutrients, an additional benefit is reduced nitrogen loss in the environment. Similar results were observed with foliar-applied humic acids on sugarcane, in which nitrogen absorption improved and reduced nutrient loss (Leite et al., 2020). Both studies indicate that combining humic acids with nitrogen fertilizer can be a powerful tool for enhancing nutrient use efficiency and management efforts.
Further research on humic acids with fertilizer applications showed positive interactions with the increased nutrient content of the leaf. In one study, foliar application of humic acids showed benefit in corn and eggplant trials (Padem et al., 1997). Similar observations were made in tomato plants when humic acids were foliar-applied, resulting in increased nitrogen and potassium content in the plant leaves (Kazemi, 2014).
Research also indicates that humic acid use is beneficial in areas where water consumption efficiency may present a production barrier on crops like wheat (Hafez et al., 2021) and potatoes (Man-Hong et al., 2020). Both trials show that humic acids enable a positive plant response to abiotic stress like drought.
ISO 19822: The new standard in humic acid testing
Amid 2020 headlines marked by political turmoil and the onset of the COVID-19 pandemic, the establishment of International Standard ISO 19822 went largely unnoticed. ISO 19822 refines how humic acids are measured by correcting for adulterants, ensuring higher accuracy and reliability. This standard marks a significant development in humic acid testing by addressing the inconsistencies of previous testing methods, which often misidentified suspended solids like clays as humic acids, leading to inflated humic acid measurements.
ISO 19822 corrects these inaccuracies, providing a more precise and reliable measure of humic acids. This advancement is crucial for manufacturers and growers alike, as it brings uniformity to a market previously plagued by varying results from multiple testing methods. Due to differences in the older test methods, the humic acids percentages could vary widely, sometimes even doubling, which made comparing products difficult.
To help consumers identify products tested with the new ISO 19822 standard, the Humic Products Trade Association introduced a certification seal. This development is a significant update for anyone purchasing products containing humic acids. By simply looking for the HPTA Test Method Certified seal, consumers can be confident that they are buying a product tested with the most reliable method available, ensuring consistent quality and performance in their fertility programs.
AAPFCO rule changes make humic acid more accessible
The recently created Beneficial Substances Model bill by AAPFCO (Association of American Plant Food Control Officials) earlier this year will impact the plant biostimulant category, including products like humic acids. This new framework was created to change state fertilizer laws in the upcoming years. Along with updated testing for humic acids, growers can expect expanded label claims that better align with the published research.
These exciting developments in the humic acids industry make incorporating humic acids into fertility plans more accessible. To get the most out of their nutrient planning, growers should update their awareness of these new developments. Recent advancements with humic acids indicate numerous potential benefits, from enhanced nutrient availability and conservation to improved water management, and increased crop yield and quality. The new humic acids testing method also offers growers greater accuracy and reliability. Ultimately, these advantages can translate to healthier plants and reduced environmental waste, improving the entire agricultural industry.
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