Organic material is important for healthy soils. It is well known that soil with no organic component is not fertile, and needs to be heavily amended in order to build soil structure, and hold the nutrients plants need in order to grow healthily. Long term use of synthetic pesticides, herbicides, and NPK fertilizers can strip soil of its organic components leading to reduced plant health. The organic material found in soil that is so important for growing healthy plants we call these beneficial substances 'humus'. "Humus is defined as a brown to black complex variable of carbon containing compounds not recognized under a light microscope as possessing cellular organization in the form of plant and animal bodies."(1) Additionally, humus does not have any one specific shape or formulation like other organic compounds found in soil, like fats, amino acids, and enzymes, etc.
In soil, HS interact with plants and the microbiome in a variety of different ways. First, HS serve as an important binder to improve the physical structure of soil. HS are large organic polymers that can bind and repel various components of soil. As a result, soils with healthy levels of HS will have more room for microorganisms to move around, and will support the pores caused when larger soil organisms, like earthworms, move around. This aids in aeration and drainage. HS are also integral into building soil clumps, and resisting compaction.
Humic acids are very weak acidic compounds that act as a neutral pH buffer in both overly acidic (low pH) and overly alkali (high pH) environments. That makes humic acid a great conditioner for many soil types. Additionally, humic substances can bind to both salts, and sulfur, helping remediate imbalances and contamination caused by improper application of soil amendments.
The complexity of HS molecules, especially humic acids, allow a complex chemical interaction with mineral nutrients in soil. It is understood that this is a result of the various binding sites and constituent organic compounds found in HS. Both humic and fulvic acids are know to chelate difficult to transport nutrients, making them more bio-available.
Humic substances are hydrophilic, meaning water likes to stick to them. Soils with healthy levels of HS will naturally hold more water than unhealthy soils, meaning plants water needs can be more immediately met. HS also facilitate water bridging, a chemical process where water is attached to another molecule, one of the ways nutrients are transported through soil and plants.
HS prevent valuable nutrients from being depleted from soil through water infiltration. "In the absence of humic substances trace minerals elements are converted to insoluble precipitates such as metal carbonates, oxides, sulfides, and hydroxides"(1). In one study, researchers noted higher levels of Nitrogen (N), Phosphorous (P), and Potassium (K), in soil treated with HA. The tested levels of NPK in these soils continued to increase over the course of the three year study, while NPK numbers decreased in the untreated control group(3).
Lastly, components of humic substances, especially fulvic acids, can mimic the effects of hormones in soil. application of fulvic acid mimics the signals that plants use to communicate with each other and the microbiome. specifically, compounds that resemble growth stimulating plant hormones have been noted contained within the structure of humic acids by numerous researchers(2). Fulvic acids are further broken down through oxidization vectors, making various different parts of the humic molecules available for chemical interaction with plant and microbe cells.
Humic Substances are beneficial for plants, and healthy, undisturbed soils have them in abundance. This is especially true in areas where minerals and nutrients are common. Many modern agricultural soils have been abused through the common modern agricultural practices of continuous cropping, mono culture, the application of synthetic fertilizers, over application of pesticides and herbicides, and over working the soil. Even modern garden soil for home gardeners is often damaged by these factors. The application of humic acids can augment any growing protocol, as humic substances provide benefits across all factors of growing plants.
In growers wishing to focus on the ecosystem of their soil, rather than only the output of their plants, humic acids are an important step in building healthy, sustainable soil. Humic substances increase soil capacity in nutrient cycling, water holding, microbial activity, and hormonal communication. Humic substances are present in bio-char, compost, and worm castings, but the best sources of humic acid are ancient deposits of long ago composted plant and animal matter. These deposits are often ancient bogs or wetlands that have decomposed and mineralized over eons. Lignite is especially desirable because once exposed to various environmental, physical, and natural chemical processes, a producer can generate higher levels of fulvic acids than other sources of humic substances.
1-Pettit, R. E. (2006). Organic matter, humus, humate, humic acid, fulvic acid, and humin. The Wonderful World of Humus and Carbon.
2-Trevisan, S., Francioso, O., Quaggiotti, S., & Nardi, S. (2010). Humic substances biological activity at the plant-soil interface: from environmental aspects to molecular factors. Plant signaling & behavior, 5(6), 635–643. https://doi.org/10.4161/psb.5.6.11211
3-Li, Y., Fang, F., Wei, J., Wu, X., Cui, R., Li, G., ... & Tan, D. (2019). Humic acid fertilizer improved soil properties and soil microbial diversity of continuous cropping peanut: a three-year experiment. Scientific reports, 9(1), 1-9.
4-Bernstein, N., Gorelick, J., Zerahia, R., & Koch, S. (2019). Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis (Cannabis sativa L). Frontiers in plant science, 10, 736.