Lecture 28 Effect of Organisms on Soil Organic Matter real

Lecture 28 Effect of Organisms on Soil Organic Matter real...

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Unformatted text preview: Effect of Organisms on Nutrient Availability Soil Organic Matter •Carbon •Hydrogen •Oxygen •Phosphorus •Nitrogen •Sulfur Soil Organic Matter Biomass: Detritus: Humus: Living organisms Identifiable dead tissue unidentifiable tissue Humic Nonhumic 60 -80% SOM Complex Resistant, High C 20 -30% SOM Less complex Less resistant Fulvic acid, humic acid, humin (Undefined, high molecular wt.) Polysaccharides, proteins, acids (defined, lower molec. Wt.) 1 Decomposition CO2 60-80% 100% Atmosphere Organic residue C 3-8% biomass 3-8% Non-humic 10-30% humic + Release of plant-essential nutrients Factors in Decomposition Factors in Decomposition Composition of the organic material Temperature/Climate Water/Oxygen Location Size Chemical Makeup 2 Composition Plants Compounds Elements Composition Effect on Rate of Decomposition Decomposition Sugars/starches (5%) Proteins (8%) Hemicellulose (18%) Cellulose (45%) Fat & Waxes (2%) Lignins and phenols (22%) Rapid decomposition Slow decomposition Effect of Climate (U.S.) Temperature: increases from N to S – Degradation increases, OM decreases, higher OM contents in soils from colder regions Moisture: increases from west to east Biomass increases, OM increases High OM: Cooler temperatures, moist conditions Low OM: Hotter temperatures , dry conditions 3 A GENERAL RELATIONSHIP Location and Size Increased decomposition Surface placement (in rather than on) Particle size (small better than large) Primary Chemical Factors Carbon to Nitrogen ratio (C:N) Near neutral pH 4 C/N Ratios The carbon content in plant dry matter is ~42% The carbon content in SOM ranges from 40 to 60% N content of plant residues ranges from <1 to >6% Why C/N RATIO IS IMPORTANT Soil microbes require C to build organic compounds in cells, and for energy. Soil microbes need N to produce amino acids, proteins enzymes and DNA for cellular metabolism. 1. 2. 2. Microorganisms compete for soil N C/N determines the rate of decay and the ultimate availability of nitrogen to soil and plants. C/N ratio in Plants and Microbes Plant residues from 10:1 to 30:1 but can be as high as 600:1 (conifer sawdust) As plants matures N ↓, lignin and cellulose↑; C/N ↑ C/N ratio is much lower in microbes (5:1 to 10:1) 5 C/N ratios of Organic Components Various C/N ratios – Soils – Microbes – Legumes – Sawdust 8/1 to 15/1 5/1 to 10/1 (high N content) 10/1 to 30/1 (alfalfa, soybeans) 400/1 to 600/1 (low N content) Influence of C/N Ratio on Decomposition Soil microbes need C to build organic compounds and for energy, BUT Soil microbes need N to produce amino acids, enzymes and DNA Soil microbes have on average 8 parts C for every 1 part N in their bodies (C:N = 8:1) Soil microbes incorporate only about 1/3 of the C metabolized into their bodies; while 2/3 is respired as CO2 Therefore, soil microbes need 24:1 ratio in their “food” food” 24 carbons/ 1 N 24 carbons 2/3 C as CO2 16 carbons 1/3 C in body 8 carbons Decomposition and Nitrogen Mineralization The release of nitrogen from The organic form to the inorganic form Organic N (Organic matter) NH4+ Low C:N is desired for high rates of nitrogen mineralization 6 Decomposition and Nitrogen Nitrification The conversion of ammonium to nitrate NH4+ Organic N Mineralization (Organic matter) NH4+ Nitrification Low lignin and polyphenols, Low C:N Release of organic N + Change in Mineralization NO3- High lignin and/or Polyphenols, low C:N 0 High lignin and/or Polyphenols, high C:N Low lignin and polyphenols, High C:N Residues added Time (weeks) For N mineralization (release) want low lignin, low polyphenol, and low C:N ratio. Addition of residues with high C:N ratio measure Microbial activity, CO2 evolved C:N ratio of residues Soluble N level in soil N depression period Residues added Time Addition of residue high in C:N ratio (> 25:1); High microbial activity; CO2 released Microbes scavenge N from the soil, depressing the soil N 7 Addition of residue with low C:N Measure Microbial activity, CO2 evolved Soluble N level in soil C:N ratio of residues Residues added Time Addition of residue low in C:N ratio (< 25:1); High microbial activity; CO2 released Getting N from the residual, increasing the soil N Addition of residues with high C:N will increase microbial activity However, there is insufficient N in the substrate for cellular growth and metabolism, Therefore, the organism will take N from soil solution depressing N in soil temporarily. Addition of residues with low C:N also increases microbial activity However, there is sufficient N in the substrate for cellular growth and metabolism, Therefore, the organism will release N to the soil increasing its levels. 8 ...
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This note was uploaded on 07/31/2011 for the course SOS 3022 taught by Professor Staff during the Fall '08 term at University of Florida.

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