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Role of Humic Acid in Improving Soil Quality and Plant Growth




  • Sustainability in agriculture is an important goal, which can be gained through the effective and economic utilization of natural resources as well as careful management of agricultural inputs. Fertilizers are the important input, which is proved to be essential for better and quality production. The rising prices, untimely availability, adequate doses and purity of fertilizers are the important considerations now days. Deficient and excessive fertilization induces ill-effects on crop health and produce quality. The fertilizer requirements of plants differ with nature and age of plant, edaphic and climatic factors. Balanced nutrients availability at the proper growth stage improves yield, quality and other growth characters. Organic matter (O.M) acts as store house of nutrients and can reduce the use of mineral fertilizers. Synthetic fertilizers are very costly and do not fulfill the farmer’s demand, so there is a need to use bio chemicals like humic acid and micro nutrients to increase yield with superior quality fruits and crops.

    What is Humus or Humic Acid? The term “humus” was later applied to the organic matter of soils and composts, or to different fractions of this organic matter as well as to complexes formed from a variety of natural organic substances. Humus compounds are complex natural organic compounds that are formed in soils from plant residues, by a process of “humification”. Humus materials are complex aggregate of brown to dark colored amorphous substances, which have originated during the decomposition of plant and animal residues by microorganisms, under aerobic and anaerobic conditions, in soils, composts, peat bogs, and water basins. Chemically, humus consists of certain constituents of the original plant material resistant to further decomposition; of substances undergoing decomposition; of complexes resulting from decomposition, either by processes of hydrolysis or by oxidation and reduction; and of various compounds synthesized by microorganisms.
    Humic acid is a fraction of humic substances composed of a long chain molecule, which is high in molecular weight and soluble in an alkaline solution. Humic acid is known to be among the most bio-chemically active materials found in soil. All humic acids are primarily composed of carbon, oxygen, nitrogen and hydrogen. They may also contain sulfur and phosphorus in varying minute amounts depending on the source.  Humic acid use will reduce the need for fertilization due to the soil’s and plant’s ability to make better use of it. In some occurrences, fertilization can be eliminated entirely if sufficient organic material is present and the soil can become self-sustaining through microbial processes and humus production.
    Impact of Humic acid on soil: Physically, humic acids modify the structure of the soil. It improves the soil structure and prevents high water and nutrient losses in light, sandy soils. Simultaneously convert them into fruitful soils by way of decomposition. In heavy and compact soils, aeration of soil and water retention is improved; cultivation measures are facilitated. Soil cracking, surface water runoff and soil erosion are prevented by increasing the ability of colloids to combine. It helps the soil to loosen and crumble and thus increase aeration of soil as well as soil workability. Soil water holding capacity increased and thus help resist drought. It makes dark color of soil and thus help absorption of the sun energy. Chemically, humic acids change the fixation properties of the soil. Humic acids neutralize both acid and alkaline soils; regulate the pH-value of soils, improve and optimize the uptake of nutrients and water by plants, increase buffering properties of soil, act as natural chelator for metal ions under alkaline conditions and promote their uptake by the roots, increases percentage of total nitrogen in the soil, reduce the availability of toxic substances in soils and liberate carbon dioxide from soil calcium carbonate and enable its use in photosynthesis. Ecologically, humic acids reduce the over-salination problem in the application of watersoluble mineral fertilizers. Humic acids are able to decrease high salt contents in soils and thus the resulting toxicities. Especially the NH4-toxicity of fertilizers containing ammonia is reduced, which is of great importance for young plants particularly. Generally, humic acids reduce root burning which comes about through excessive salt concentrations in soils after fertilization; in case of permanent high levels of salt in soils, these are reduced. Furthermore, when humic acids are mixed with liquid fertilizers, the undesirable smell is diminished. They are also an effective mean to fight against soil erosion. This is achieved both by increasing the ability of soil colloids to combine and by enhancing root system and plant development. It offers an economical and effective solution to environmental problems.

    Impact of humic acid on seed: Humic acid increases germination and viability of seed by inducing enzyme production, stimulating respiration in mitochondria, increasing oxidative phosphorylation, increasing seed membrane permeability and better root growth and vigor of seedling.

    Impact of humic acid on plant: Humates have been shown to provide a significant increase in crop yields when combined with your current fertilizer program. Humates can improve root development, total leaf area and total crop yields per acre. A consistent result from all crops tested was increased root growth. Length, density, and radius of plant roots dramatically increased. Tests have shown that root system vigor is very important to the nutrient uptake capability of plants, as well as to the plant’s ability to combat disease. In addition, plant stability is enhanced, and plants are better able to find and absorb water with a broad based root system. Humic matter has been shown to increase the chlorophyll content in plants, and can prevent or correct chlorosis. Humates have been shown to consistently improve the uptake of nutrients such as nitrogen, phosphorus, and iron, as well as innumerable trace elements essential for plant health. This is due to the biochemically active nature of humic acid, and its ability to form both soluble and insoluble complexes with various metals, minerals, and organics. Nutrients are mobilized in forms that the plants can accept. They can improve the quality of fruit, vegetables, and flowers by improving their physical appearance, and in the case of food crops, their nutritional value. Cereal crops have shown more balanced amino acid content, and higher protein content. All of this can enhance their worth in the marketplace. The biochemically active nature of humic acid is to enhance a plant’s natural defenses against toxins and disease. Many toxins are inhibited or neutralized directly by bonding interactions with humic acids. In addition, biologically active compounds (such as antibiotics and phenolic acids) found in healthy humus can enhance plant resistance to some diseases.
    In crux, some Pakistani scientists reported that best economic results can be obtained in light and sandy soils poor in humus as well as on recultivation fields. This is true for almost all soils in dry and warm regions. As a result of the high mineralization rate of organic substances, providing these soils with stable humic acids is indispensable for the maintenance and improvement of soil fertility. High increases up to 70% in yield, accompanied by a reduction up to 30% in the use of fertilizers and pesticides, as well as better and healthier growth of greengrass, ornamentals, agricultural crops and woods can be attained with the regular application of first-quality humic acids. It also reported that humic culture increased yield up to 200-500 kg ha-1 and thus 30 to 50 kg of superphosphate can be saved. In 2011, Pakistan economy positive impact of 6.5 billion rupees is estimated as a result of yield increases and saving of phosphate fertilizer by application of humic acid.

    About Author:

     Asif Ameen

    M.Sc. (Hons.) Agriculture – Agronomy

    University of Agriculture, Faisalabad – Pakistan

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