Building up humus for climate protection
In times of climate change already noticeable in our temperate zone, such a widespread substance as "humus" is once again receiving prominent social attention in the public discussion on appropriate mitigation measures. "Humus" is probably one of those natural substances that is associated with the most positive properties in its social consideration.
But what is actually understood scientifically by the term "humus"?
The textbook of soil science gives the following answer:
"The totality of the organic substances of the soil forms the humus, although other authors limit this term in part to the humic substances. On the one hand, humus is mixed with the mineral body in the soil, and on the other hand, together with the litter, it forms the supporting humus of many soils. The terms arg. Substance and humus form synonyms in this book."
And further on humic and litter substances:
- "Humic substances, highly transformed, high molecular weight substances without recognisable tissue structures."
- "Scattering substances that are not or only weakly transformed and in which the tissue structures are largely still morphologically visible. These include above-ground dead plant remains as well as dead roots and soil organisms or their components. These substances, often referred to as non-humic substances, essentially contain lipids, lignin and polysaccharide fragments.
In simple terms, humus consists of nutritive humus and permanent humus. While the nutritive humus in the form of the organic substance biomass added to the soil (i.e. essentially biomass consisting of carbohydrates, lipids, proteins and lignins) can still be biodegraded to a large extent with the release of important nutrients, the permanent humus in the form of the high-molecular humic substances is largely resistant to biological degradation. This is probably due on the one hand to the complicated macromolecular structures of the humic substances, and on the other hand to their ability to bind stably with the surrounding inorganic soil matrix in the form of stable clay-humus complexes. By binding the nutrient humus to the degradation-resistant permanent humus, microbial degradation is decisively decelerated so that a larger proportion of the nutrient humus is converted into permanent humus and, at the same time, due to the decelerated metabolism of the nutrient humus, CO2 emissions from agriculturally cultivated land are decisively reduced.
According to this traditional doctrine in German soil science, however, the functions of the various largely degradation-stable humic fractions (humic, humic acids and fulvic acids) are not limited to humus enrichment in the soil and the resulting reduction of CO2 emissions. From a simplified point of view, humic substances function as a sponge for water and nutrients in fertile soils, with the mobile, water-soluble fulvic acids additionally serving to transport nutrients. Due to their enormous adsorption capacity, humic substances also simultaneously immobilise inorganic and organic pollutants such as heavy metals and pesticide residues, thereby largely removing them from our nutrient cycle. They thus have the function of a traffic policeman in the soil, so to speak.
The sufficient availability of the globally scarce macronutrient phosphorus and many essential micronutrients such as iron, zinc, manganese and copper to plants also depends to a large extent on the humic content of a soil. Humic substances thus make a decisive contribution to improving fertiliser efficiency. In addition, humic substances reduce the emission of climate-damaging ammonia and hydrogen sulphide from farm fertilisers such as liquid manure and fermentation residues from biogas production. Humic substances can also make a decisive contribution to reducing nitrate inputs into groundwater.
Humic substances have a stress-reducing influence on abiotic, climate-related factors such as heat, drought, cold, wetness, frost and salinisation in many ways. Although these functions have not yet been sufficiently researched, decades of practical experience have shown that they have a mitigating effect on drought and salinisation, which can be explained primarily by their water-holding capacity and their buffering effect under strong osmotic pressure. In addition, the use of humic acid extracts has been shown to qualitatively and quantitatively improve the germination rate of a wide variety of seeds.
Unfortunately, degradable humic substances are only formed in very long natural biotic and abiotic processes. Despite many attempts, permanent humus cannot yet be produced synthetically in the short term, let alone industrially under economically reasonable conditions. In addition to humus-rich soils, humic substances are also found in bogs and fossil sediments in the form of peat and lignite. Due to their high degradation stability, lignite-based humic substances fulfil the requirements for permanent humus excellently. In contrast to biomass as nutrient humus, lignites do not decompose microbially to CO2 and water, but merely absorb oxygen into their molecular structure. This natural weathering process only increases the humic acid content and these weathered humic sediments are called international Leonardite. Due to the high similarity of the natural substance Leonardite with the recent humic substances in soils and the high biological degradation stability, it shows the best suitability of all currently available raw materials in the function of permanent humus.
Water-soluble concentrated humic acid extracts from leonardite and aquatic fulvic acids are already used worldwide as biostimulants in unfavourable climate and soil conditions for the purpose of climate-adapted agriculture. Climate-related abiotic stress factors include heat, drought and salt stress, but also wetness, frost and cold. Humic-based biostimulants such as humic and fulvic acids serve to increase the tolerance of crops to these abiotic stress factors. Humic and fulvic acids, for example, are able to decisively reduce the salt concentrations in the soil solution through their adsorption capacity and thus enable higher-yielding agriculture through the lower salt-induced osmotic pressure on the plants.
At the same time, humic and fulvic acid-based biostimulants increase the fertilisation efficiency of macronutrients such as phosphorus, nitrogen and potassium. Humic substances play a decisive role in the soil, especially for the plant-available mobilisation of mineral phosphates. In addition, humic substances mobilise essential trace nutrients such as iron, zinc, copper and manganese, which otherwise cannot be directly absorbed by crops, especially in dry soils poor in humus. The complexation of these trace nutrients by natural humic acids is an excellent alternative to persistent synthetic chelates such as EDTA. The adsorption of ammonium nitrogen by humic substances reduces emissions of the greenhouse gas ammonia from farm manures such as slurry and digestate, while at the same time helping to reduce nitrification and thus nitrate inputs into groundwater. Leonardite-based humic substances thus make a decisive contribution to the implementation of the European Green Deal and the agricultural strategy "From Farm to Fork".
Beyond soil improvement and plant nutrition, Leonardite-based humic substances are successfully used in environmental protection for the immobilisation of pollutants in the soil, for wastewater treatment of organic and inorganic pollutants, and for biogas desulphurisation.
In animal breeding, Leonardite is used as a feed and in medicine, humic substances are used as adsorbents for detoxification, e.g. for aflatoxins in cow's milk. In aquacultures, humic substances are used for water treatment. And natural Leonardite-based humic substances are also used in classic industrial sectors such as the battery, paper and ceramics industries. Thanks to ever new research approaches in the context of eco-adaptive chemistry, more and more ideas for sustainable use are being added.