# Methods for Obtaining Humus Substances: Advantages and Disadvantages
## 1 Introduction  
The increase in light soils and the low production potential of soils worldwide create the need to seek a way to improve their quality. The extensive use of mineral fertilizers contributes to the accelerated mineralization of organic matter and soil humus, causing the degradation of agricultural soils. There is a significant need to develop new types of artificial humic substances, which are crucial for sustainable agriculture, especially in improving soil fertility and plant growth. Using mineral fertilizers on light soils may disturb the soil environment balance and contribute to soil and groundwater contamination [1]. Humus substances (HS) of a natural origin (decomposition products of natural organic substances) are an excellent source of permanent organic substances for light soils. Regardless of their origin or location, HSs are always composed of the following elements: carbon, oxygen, nitrogen, and sulfur. HS extracted from soil generally contains about 41-51% C, 40-50% O, 3.8-7.0% H, 0.9-3.3% N, and 0.1-3.6% S [2]. In the aquatic environment, HSs transfer organic and inorganic pollutants, including heavy metals, pharmaceuticals, and other substances, threatening water systems and aquatic and terrestrial organisms' health. They become precursors of carcinogenic, mutagenic, and teratogenic substances in surface waters due to UV radiation and in water treatment plants during oxidation and disinfection [3]. However, HSs are fundamental to plant development and direct stimulation in the soil. They contribute to the transport of micro and macro elements to the root mass, increase the permeability of the cell membrane, and activate specific physiological processes of plants [4; 5]. They also significantly impact germination and root development, increase resistance to abiotic stress [6; 7; 8; 9], and increase chlorophyll production. In soil, HS form complexes with metals and microorganisms, which benefits plant growth and tolerance to metal pollution [10; 11]. The fertilizer can be a mixture of compounds composed of humic acid, citric acid with tartaric acid or humic acid, citric acid, tartaric acid with EDTA, trace elements, stabilizer (urea), matrix substances, a stringiness agent, plant growth regulator and N.P.K. nutritional elements, and iodine. The liquid fertilizer is characterized by good water-solubility, a lower temperature during preparation reaction, a higher effect of fertilizer, and much higher productivity (increased by 16-66%). It also increases drought, cold, and alkali resistance and prevents and/or controls plant diseases and insect pests [12]. Therefore, in recent years, many methods have been developed to obtain HS from various substances, such as sodium lignocellulosic, brown coal, and municipal waste. Many patents have been filed regarding HS extraction methods [13], from methane fluid [14; 15], humic acid and fulvic acid from humus substances [16; 17], fulvic acid from humus substances generated from peat, marine diatomaceous, plankton [18], humin-mineral concentrate from a water suspension which comprises humic acid salts and fine humin-mineral particles and complexes [19], humic substances from leachate from municipal solid waste or similar [20], humus substances from soil [21; 22], humus acid from kitchen waste [23], from plants containing lignin [24], fertilizer from concentrated yeast cream waste liquid [25], from a mixture of raw materials (by weight): 34% to 36% of plant straw, 5% to 7% of cake fertilizer, 5% of waste from production monosodium glutamate, 7% of distillers' grain, 20% of dry, not polluted pond sludge, 8.5% of grass carbon, 1% of organic fertilizer leavening agent, 1% of sterilizing deodorant, 8% of ammonium sulfate, 8% of mono-ammonium phosphate [26] and from other raw materials. There are many different raw materials (leonardite, lignite, humalite, brown coal, and sub-bituminous coal), but they all essentially refer to the same thing.