NRES 201 Lecture 14 Outline of Last Lecture I. Soil Management and Bulk DensityII. Soil PorosityIII. Aggregate formation and stabilization Outline of Current Lecture IV. What is soil organic matter? (SOM)V. Functions of soil organic matterVI. Soil organic matter managementVII. Decomposition in soilsVIII. Factors affecting soil content and distribution of organic matterIX. The global carbon cycleCurrent LectureSoil Organic Matter - The organic component of soil consisting of: Living organisms (biomass), Organismal remains (residues), Decay products (Humus)- Estimated from soil organic C (SOC)o SOM = SOC x 1.8o Excludes inorganic C in carbonates Functions - - Nutritional functionso Energy and C source for heterotrophic microbeso Supplies N, P, and S to plants and microbeso Increases nutrient - holding capacity - Physical functionso Improves soil structure, aggregation, and macro porosity Critical for temperate soilso Enhances water infiltration and aeration o Increases water holding capacity o Reduces erosion and compaction- Biological functionso Essential for all heterotrophs including: most microbes, macro and micro fauna - Ecological functionso SOM is the Earth's major surface C reservoir These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Soil Organic Matter Management- Need to balance opposing factorso SOM decreases when residue decomposition is greater than residue inputo SOM increases when residue input is greater than residue decomposition- Residue inputs increased byo High crop yields with: Improved varieties, high planting rates, optimal fertilizer use, and adequate crop production practices - Decomposition decreased by:o Reduced tillageo Less decomposable residues having: A higher C/N ratio or a higher lignin contento Avoiding excessive N or P fertilizationo Fine textured soilDecomposition in Soils- Organic constituents and their ease of decomposition o Most decomposable - Sugars, starches, crude protein, fats, lignin- Dynamics of decomposition o For residues with a high C/N ratio (corn stalks) Decomposition is prolonged N is tied up (immobilized) Plant N availability is depressedo For residues with a low C/N ratio (alfalfa tops) Decomposition is rapid N is liberated (mineralized) Plant N availability increaseso Rate of decomposition Faster with a low C/N ratio Slower with a high C/N ratioFactors affecting soil content and distribution of organic matter:- Pedologic factors - temperature and moisture regime, type of vegetation- Soil textureo More organic matter in fine - textured soils because: a higher water content reduces aeration, clay protects organic matterManagement practices:- Tillage and drainage promote the loss of soil organic matter by stimulating microbial
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