MK Villarin Module 7 - Answer
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Visayas State University Main Campus - Baybay City, Leyte**We aren't endorsed by this school
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SOIL 22
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Biology
Date
Jan 8, 2025
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4
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Ma Kris Villarin07-1-00164Module 7: AnswersModule 7: Soil Organic Matter1.What is the major source of soil organic matter? – Plant Residue2.Which is the most dominant pool of SOM, in terms of amount in the soil?3.This form of SOM is largely responsible for the large contribution of SOM to CEC. -Humus4.This pool is SOM is largely responsible for improving soil structure.5.True or false. When an organic material has a high C:N ratio, it decomposes easily. –FalseLearning Tasks/Activities1.Visit 2 areas near your place, where there is very obvious difference in SOM content,1 high and 1 low. Prepare a write-up to describe and compare these 2 soils in termsof the vegetation, physical properties, and any other important observations that youcan give. Maximum length is 1 page. Also take pictures and send with your write-up.
Ma Kris Villarin07-1-00164Module 7: AnswersSoil organic matter is made up of a variety of components. These include, in varying proportions and in many intermediate stages, an active organic fraction, including microorganisms (10-40 per cent) and resistant or stable organic matter (40-60 per cent), also referred to as humus. Though both soil exhibit an acidic soil still, Soil B exhibit more Soil Organic Matter. This might be the vegetation status of the soil. Since majority of soil organic matter originates from plant tissue and soil B contain more of the vegetation. Plant residues contain 60-90 per cent moisture content. The remaining dry matter consists of carbon (C), oxygen, hydrogen (H) and small amounts of sulfur (S), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg). Although present in small amounts, these nutrients are very important from the perspective of soil fertility management. Due to its acidity, Soil A weeds and other grasses tend to live in this kind of soil. Coconut trees are visible but less compared to Soil B. This probably the acidity of the soil. Soil A is more acidic compared to Soil B. Thus the vegetation availability is more in Soil B. Soil A B Vegetation Upland Rice, Coconut, Grass, Weeds Coconut, Fruit Trees, Corn (elevated) Color Reddish Reddish Texture Clay Clay loam Organic Matter based on RSL 8 Analysis 1.93% (Low) 3.96% (High) pH based on RSL 8 Analysis 5.32 6.56 Observation Wet soil due to rain Dried and compact soil (previous land fill) A B
Ma Kris Villarin07-1-00164Module 7: AnswersAssessment1.Discuss briefly how C/N ratio affects the rate of decomposition and nutrientavailability in soils.The C:N ratio of organic residues added to soil is important because it influences therate at which a residue decomposes and the amount of nitrogen recycled from theresidue. This relationship occurs because bacteria, the major microorganisms ofdecomposition in most terrestrial and aquatic soils, contain about 10 percentnitrogen, and they typically convert about 10 percent of the organic matter in aresidue to bacterial biomass on a dry matter basis.When bacteria decompose in 100 kg of organic matter that contains 2 percentnitrogen, 10 kg of bacterial biomass containing 1 kg of nitrogen will result. Theresidue contains 2 kg nitrogen – more than that needed by bacteria to decompose it.The excess 1 kg will be released into the environment as ammonia nitrogen.On the other hand, suppose the residue contains only 0.5 percent nitrogen. Therewould be only 0.5 kg nitrogen in the residue – not enough to allow bacteria to quicklydecompose it. In this case, one of two phenomena will occur.The bacteria could remove and immobilize nitrogen from the surroundings todecompose the residue. But, if the environment is deficient in nitrogen, the residuewill decompose slowly, because part of the nitrogen necessary for decomposing itmust come from recycling. Bacteria have to die and be decomposed for their nitrogento be released for reuse in degrading the residue.Residues with carbon-nitrogen ratios of 20:1 to 30:1 decompose quickly andcompletely, and release through mineralization considerable nitrogen. The additionof such residues does not result in an increase in the soil organic matterconcentration.The addition of residues with low C:N ratios sometimes leads to the breakdown ofolder organic matter in the soil, whose decomposition rates were formerly limited byinsufficient nitrogen. A residue with a C:N ratio greater than about 20:1 usuallydecomposes slowly unless there is abundant nitrogen in the environment tosupplement that of the residue. This type of residue causes soil organic matterconcentration to increase.
Ma Kris Villarin07-1-00164Module 7: Answers2.Briefly discuss the importance of each SOM pool in relation to soil physical andchemical properties.Organic matter plays an important and multifaceted role in soil. Physically, organicmatter affects the structure of the soil and all its associated properties. Chemically,soil organic matter affects cation exchange capacity and soil pH buffering capacity.Biologically, organic matter acts as a nutrient and energy supply for microbialbiomass and higher plants. A soil that is biologically and chemically fertile but cannotphysically support crop development will not fulfill its agronomic potential. As aresult, soil productivity is determined by a combination of the influence of organicmatter on physical, chemical and biological soil properties.Physical Properties. Soil physical properties affected by SOM include bulk density,aggregation, water retention and movement, air composition, and heat capacity andtransmission. Soil physical processes impacted by SOM content include crusting,compaction, water runoff, erosion, gaseous diffusion, and nutrient transformationand movement.Chemical Properties. SOM increases soil fertility by providing cation exchange sitesand being a reserve of plant nutrients, especially nitrogen (N), phosphorus (P), andsulfur (S), along with micronutrients, which the mineralization of SOM slowlyreleases. As such, the amount of SOM and soil fertility are significantly correlated.3.Give 3 practical methods in which you can contribute in building up SOM in yourarea/farm/locality3.1 Composting of dried plant tissues and other residues3.2 Using green manure3.3 Crop Rotation