Organic Matter Decomposition Lecture Notes PDF

CSU1168: Soil microbes Lecture: Organic matter decomposition  SOIL ORGANIC MATTER Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus (bodies or fragments of bodies of dead organisms and fecal material) at various stages of decomp...

CSU1168: Soil microbes Lecture: Organic matter decomposition  SOIL ORGANIC MATTER Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus (bodies or fragments of bodies of dead organisms and fecal material) at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous benefits to the physical and chemical properties of soil and its capacity to provide regulatory ecosystem services. SOM is especially critical for soil functions and quality.  SOM also acts as a major sink and source of soil carbon (C). Although the C content of SOM varies considerably, SOM is ordinarily estimated to contain 58% C, and "soil organic carbon" (SOC) is often used as a synonym for SOM. The concentration of SOM in soils generally ranges from 1% to 6% of the total mass of topsoil for most upland soils. Soils containing 12% to 18% SOC are generally classified as organic soils.  The mineral products are: Element Mineral Products Carbon CO2, CO32−, HCO3−, CH4, C NH4+, NO2−, NO3−, N2 (gas), Nitrogen N2O (gas) Sulfur S, H2S, SO32−, SO42−, CS2 Phosphorus H2PO4−, HPO42− H2O, O2, H2, H+, OH−, K+, Others Ca2+, Mg2+, etc.  Humus ❖As vegetal detritus decomposes, some microbially resistant compounds are formed, including modified lignins, oils, fats, and waxes. Secondly, some new compounds are synthesized, like polysaccharides and polyuronids. These compounds are the basis of humus. ❖Humus is the dark organic matter that forms in soil when dead plant and animal matter (including aerobic compost) breaks down further, specifically through the action of anaerobic organisms. ❖ The ratio of carbon to nitrogen (C:N) of humus is 10:1. Humic acids/substances Humic acids/substances are classified into 3 genera based on their solubility in acids and alkalis, and also according to their stability: Fulvic acid is the genus that contains the matter that has the lowest molecular weight, is soluble in acids and alkalis, and is susceptible to microbial action. Humic acid is the genus that contains the intermediate matter that has medial molecular weight, is soluble in alkalis and insoluble in acids, and has some resistance to microbial action. Humin is the genus that contains the matter that has the greatest molecular weight, is the darkest in color, is insoluble in acids and alkalis, and has the greatest resistance to microbial action. Benefits of Stable Soil Organic Matter Physical Benefits Enhances aggregate stability, improving water infiltration and soil aeration, reducing runoff. Improves water holding capacity. Reduces the stickiness of clay soils making them easier to till. Reduces surface crusting, facilitating seedbed preparation. Chemical Benefits Increases the soil’s ability to hold onto and supply over time essential nutrients such as calcium, magnesium and potassium. Improves the ability of a soil to resist pH change; this is also known as buffering capacity. Accelerates decomposition of soil minerals over time, making the nutrients in the minerals available for plant uptake. Biological Benefits Provides food for the living organisms in the soil. Enhances soil microbial biodiversity and activity which can help in the suppression of diseases and pests. Enhances pore space through the actions of soil microorganisms. This helps to increase infiltration and reduce runoff. Sugar+O 2 CO +H O 2 2  Hydrolysis/ Aminization Ammonification Proteases Proteins Peptones Amides Ammonia  Cellulase Cellobiase Cellulose Cellobiose Glucose Amylose Amylose  Amylase Alpha glucosidase Starch Maltose Glucose Dr. Jyoti Mehta Assistant Professor School of Biotechnology. Shoolini University Village Bajhol, Solan (H.P) [email protected]