The Importance of Fulvic and Humic Acids in Nitrogen Absorption

By: Eduardo Morales Casas 

Did you know that fulvic and humic acids are highly favored in commercial production?

We conducted a trial in Brownsville, TX, to test the efficiency of fulvic and humic acids, where the treatments were the comparison of a traditional, commercial fertilization and the same fertilization plus the addition of Fulvic and Humic Acids. The trial lasted 105 days in which crops were evaluated in four different plant stages, measuring NO3– and K+ absorption, observing the physical state of the plants. The results show that the use of fulvic and humic acids is highly favorable, especially for commercial production.

The objective of this trial is to analyze the importance of fulvic and humic acid application in oat fertilization, observe its development and the absorption of nitrogen in different plant stages and its production in dry and wet matter.

The Importance of Nitrogen and Fulvic and Humic Acids in Plant Nutrition

Nitrogen in Plants

Nitrogen is one of the essential macronutrients for the growth and development of any crop. The soil naturally has it in organic and mineral form, the latter being essential for plant absorption. However, the amounts available in soil do not suffice to meet the needs of cultivated plants, which is why fertilizers must be applied to provide the missing nitrogen.

Nitrogen is part of proteins, enzymes and chlorophyll, thus being essential in both protein synthesis and photosynthesis. Its functions also include accelerated cell division and root elongation; therefore, it is important to consider that a plant that lacks nitrogen will not be able to complete the metabolic processes essential for its growth.

It should be noted that it also intervenes in various processes such as cell division and chlorophyll production, without which photosynthesis is not possible. Nitrogen plays a key role in the production of sugars, starch and lipids, among other essential substances for nutrition and basic plant processes.

Nitrogen moves into the root system by mass flow. The forms that can be assimilated by plant roots in the soil are nitrate NO3-) and ammonium (NH4+). In the majority soils, the action of nitrifying bacteria causes crops to absorb more nitrate; whereas, in other special soil situations, such as anaerobic conditions, plants take up relatively more ammonium than nitrate.

The Importance of Fulvic and Humic Acids in Plant Nutrition

Fulvic and humic acids are complex macromolecular groups in which the main units are aromatic compounds phenolic in nature proceeding from the decomposition of organic matter and nitrogen compounds cyclical and aliphatic synthetized by some microorganisms present in the soil.

The origin of fulvic and humic acids derives from various sources, mainly from the decomposition of peat and plant remains, but the most important is derived from Leonhardite.

The humus is essentially formed by two acids: humic and fulvic; the main difference being their behavior in acidic solutions: humic acids are not soluble in basic solutions and for this reason they precipitate; while fulvic acids remain soluble all the time.

Classification of Soil Organic Matter Components: Physical and Chemical Criteria.

Source: Brady & Weil, 2002.

Fulvic acids constitute a series of solid and semi-solid amorphous compounds, yellowish in color and colloidal in nature, easily dispersed in water and are not precipitable by acids.

The natural benefit of fulvic acids in plants, either by direct application to the soil or by foliar application, is the increased resistance to biotic and abiotic agents, such as resistance to diseases and stress conditions like drought, frost and attacks of certain pests, which can only be achieved through continuous applications.

In addition, in the metabolic system of plants, fulvic acids provide enhanced respiration, increased protein metabolism and the activity of multiple enzymes, enhancing the permeability of cell membranes, cell division and elongation. They are also very important in chlorophyll synthesis.

As for the direct effects on the soil, fulvic acids are necessary to stabilize soil pH, assist nitrification by bacteria fixation and contribute to the electrochemical balance of both the donor and the recipient. They also have action on silica in terms of its assimilation, helping the release of some essential minerals and having a detoxifying action on the soil, mainly from pesticides and herbicides.

The main benefits obtained by applying fulvic acids are:

  • Stimulate overall plant growth.
  • Perfect nutrient and agrochemical absorption and translocation, both in foliar application and to the soil or root.
  • Enhance soils by promoting microorganism reproduction.
  • Act as biostimulants and catalysts for biochemical processes in plants and the formation of nucleic acids, due to their high amino acid content.
  • Perform chelating actions and make the nutrient that is difficult to absorb available to the plant.
  • Stimulate the development of pesticide- and herbicide-degrading microorganisms that usually settle in the soil for a long time.


Oats are an annual herbaceous plant, belonging to the grass family. They are autogamous, the degree of allogamy rarely exceeding 0.5%. The majority of cultivated oats are hexaploid, Avena Sativa being the most cultivated, followed by Avena Byzantine; although Avena Nuda, also known as naked oats, is also frequently cultivated as the glumes are shed when threshed.

The botanical characteristics of the group of hexaploid oats are mainly the articulation of the first and second flower of the spikelet, the naked or clothed nature of the grain and the morphology of the edges.

Roots: a powerful root system, with more abundant and deeper roots than those of other cereals.

Stems: thick and straight, with little resistance to lodging, good forage value. Stem length can vary from half a meter to one and a half meters. They are formed by several internodes that end in thick nodes.

Leaves: flat and elongated. At the junction of the blade and stem, they have a ligule, but no stipules. The ligule is oval and whitish, with a toothed free edge. The leaf blade is narrow and long, semi-dark to dark green, rough appearance, with numerous hairs at the base. The nerves of the leaf are parallel and quite marked.

Flowers: the inflorescence is in a panicle. It is a cluster of two- or three-flower spikelets, located on long peduncles. Anther dehiscence occurs when flowers open. However, there is a certain proportion of flowers that open their glumes and husks before stamens and pistil mature, consequently causing the degeneration of selected varieties.

Fruit: caryopsis, with the glumes attached.

Materials and Methods

Seeds were sown in an area of ​​350 ft2 in the Ferti-Organic experimental field, located in Brownsville, TX. The sowing rate was 1 lb, approximately 14,660 seeds per 10 ft2, of the organic OATS (common) variety from Johnny’s Selected Seeds Company.

Seed Characteristics and Sowing Specifications

  • It presents early maturing and good standing with very high yields.
  • Ideal for underseeding with a legume.
  • Oats are a quick-growing green manure.
  • USDA-certified organic
  • Average 14,660 seeds/lb.

For winter cover, sow by early September in the North, slightly later farther south; the heavy stubble will prevent erosion and oats will not regrow in the spring like winter rye. For grain production, seeds should be sown in early spring for a late summer crop. Sowing should be 3-4 lb/1,000 ft2, or about 150 lb/acre.

For the purposes of this trial, seeds were fertilized at a rate of 170-67-240 according to the TPSL laboratory recommendations located in Edinburg, TX. The following fertilizers were used: Ammonium sulfate, Triple 17, Osmocote slow release 14-14-14, MAP and STEM as a source of microelements and fulvic and humic acids.

The irrigation system was drip, with a Dosatron fertilizer injector.

  • Treatment 1: traditional fertilization.
  • Treatment 2: traditional fertilization plus fulvic and humic acids (50 g of each in 4 applications).

Characteristics of Fulvic Acid to be Used

  • Fulvic Acid is a concentrate derived from plant residues.
  • This high-efficiency, multi-functional fertilizer is ideal to aid plant uptake of micronutrients.
  • It is compatible with most liquid fertilizers, pesticides, herbicides and defoliants.
  • It possesses the same characteristics and benefits of Fulvic Acid 90% with a lower concentration (70%).
  • A compatibility test is advised before application.

Characteristics of Humic Acid to be Used

Humic substances are end products of microbial decomposition and chemical degradation of dead biota in soils. Considered to be the most abundant naturally occurring organic molecules on earth and the major components of soil organic matter, they are considered plant biostimulants.

Humic Acid is the potassium salt of humic acid also known as potassium humate. It has all the characteristics of humic acids, with the additional benefits of solubility without precipitation or solid separation after dilutions are made.

It has a minimum of 70% humate matter, including fulvic acids which remain in the solution as long as necessary. Humic substances play key roles in many soil and sand plants such as controlling nutrient availability, carbon and oxygen exchange between the soil and the atmosphere, as well as transforming and transporting toxic chemicals; in addition to increasing overall root growth at early stages of plant development. Humic acids have also been found to increase crop yield and quality in some studies involving full-season plant growth in greenhouses and fields.

For the purposes of this trial, measurements were carried out at 60, 75, 90 and 105 days, determining the parameters below:

  • NO3– concentration expressed in ppm.
  • K+ concentration expressed in ppm.
  • Na+ concentration expressed in ppm.
  • Ca+ concentration expressed in ppm.
  • Amount of oats per ft2 in green.
  • Obtaining dry matter.

The instruments used to measure were HORIBA LAQUAtwin and brixx meter. Dry matter was obtained by manual dehydration method with microwave oven.


After observing greater NO3– absorption in the four different plant stages, we were able to obtain an increase of 12.90% at 60 days, of 39.39% at 75 days, of 18.39% at 90 days and of 23.23% at 105 days, parts per million (ppm).

This can be seen in the graph below:

Graph 1. Absorption.

Source: Personal Research (2022).


The amount of production of 1 ft2 in each physiological plant state, the percentage of dry matter, the green production per ft2 and the total production of dry matter per acre were obtained, obtaining the results shown in the table below:

Table 1. Green oat production per ft2. Source: Personal Research (2022).

Graph 2. Oat production.

Source: Personal Research (2022).

Table 2. Dry matter.

Source: Personal Research (2022).

Graph 3. Dry matter.

Source: Personal Research (2022).

Table 3. Total production of dry matter.

Source: Personal Research (2022).

Graph 4. Total production.

Source: Personal Research (2022).


As it is clearly striking, we can conclude that fulvic and humic acid application in fertilization promotes increased production, observing plants with greater vigor.

There were no iron chlorosis issues in the plot treated with fulvic and humic acids; however, greater resistance to oat rust and lodging was found. We achieved adequate fulvic and humic acid application in oat fertilization, observing both its development and nitrogen absorption in different plant stages and its production in dry and wet matter, which is why we advise replicating said trial with an extremely favorable result.


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Inter-American Commission for Organic Agriculture (ICOA). (2022). Official site.

García, M.E. and Bermúdez, G. (2014). Alimentos sustentables, de la Tierra a la Mesa. Mexico: CONABIO/Calmil Comunicación.

Johnny’s Selected Seeds. (2022). Avena, semilla de cultivo de cobertura orgánica. Producer’s Library.

Ferti-Organic. (2022). Official site.

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