- Macrofauna
- Vertebrates(gophers, moles, rodents etc.)
- Annelids
- Earthworms
- process upto 15 tons/A/Y
- casts weigh up to 16,000 lbs/A
- improve aeration and drainage
- plow in organic matter
- prefer moist, aerated, finer textured soils with pH around 6.5
- biomass of 100 - 1000 lbs/A
- process upto 15 tons/A/Y
- Earthworms
- Arthropods (insects, arachnids, crustaceans)
- ants, termites, beetles, grubs, centipedes
- early breakdown of organic matter
- add to total soil organic matter
- ants, termites, beetles, grubs, centipedes
- Mollusks(snails,slugs)
- Vertebrates(gophers, moles, rodents etc.)
- Microfauna
- Nematodes(threadworms, eelworms)
- Rotifers
- Protozoa(Amoeba)
- Nematodes(threadworms, eelworms)
- Microflora
- Bacteria
- Simple, single celled microbes, most are heterotrophic although there are many that derive energy from autotrophically from chemical reactions.
- most numerous microbes in the soil -- 107 to 108 per gram of soil
- have a very diverse physiology-- anaerobic and aerobic
- populations are dependent on food source and environment.
- Simple, single celled microbes, most are heterotrophic although there are many that derive energy from autotrophically from chemical reactions.
- Actinomycetes
- intermediate between bacteria and fungi-- now classified as bacteria.
- filamentous bacteria
- 2nd most abundant organism in the soil (over 1 million / gm)
- decompose resistent organic compounds(cellulose and chitin)
- like pH 6-7.5
- some fix Nitrogen
- give soil its rich earthy smell
- some produce antibiotics(streptomyces)
- intermediate between bacteria and fungi-- now classified as bacteria.
- Fungi
- no chlorophyll -- heterotrophic organisms(energy from organic compounds)
- fungi are fewer in number than bacteria but make up the largest biomass of any microbe in soils. A mass of hyphae is called mycelium. Mushrooms are the fruiting bodies of fungi.
- yeasts (not very important in soils)
- mushrooms
- Molds (widest pH range)
- dominate at low pH due to reduced competition
- often have the greatest biomass of any soil microbe
- decompose cellulose, lignins and complex organic compounds
- mycorrhizal fungi- colonize plant roots in a symbiotic relationship utilizing carbon from the plant while benefitting the plants by increasing uptake of phosphorus and possibly other nutrients and water.
- no chlorophyll -- heterotrophic organisms(energy from organic compounds)
- Algae
- contain chlorophyll and are photosynthetic. They are autotrophic orgaisms
- primary producers
- live near the soil surface
- found in moist to wet soils at or near a neutral pH.
- contain chlorophyll and are photosynthetic. They are autotrophic orgaisms
- Bacteria
- Environmental Factors affecting Microorganism populations
- Moisture Content: Moist soils around -1 bar are ideal for microorganisms. Soil moisture conditions too dry or too wet inhibit growth.
- Adequate Temperature Range: Activity of microorganisms is limited below 5 degrees C (45 degrees F).
- Adequate Carbon: Organic matter is a food source. Different organisms use different types of organic matter
- Adequae Soil pH: Different microorganisms work in specific pH ranges.
- Proper Competing Organisms: Microbes are particular to the types of orgnisms that are around them.-- by planting certain types of plants different types of organisms may be controlled.
- Aeration: There are aerobic and anaerobic organisms
- Heterotrophs
- get energy and carbon from organic compounds
- most numerous types
- includes nitrogen fixing bacteria
- get energy and carbon from organic compounds
- Autotrophs: obtains energy comletely from the oxidation of inorganic elements or compunds such as iron, sulfur, hdrogen, ammonium and nitrates or from radiant energy
- don't require organic source for energy
- oxidize S and NH4+ for energy (inorganic material)
- obtain C from CO2
- includes nitrifying bacteria
- Heterotrophs
- Moisture Content: Moist soils around -1 bar are ideal for microorganisms. Soil moisture conditions too dry or too wet inhibit growth.
- Organic Matter
- Definition: living or dead plant or animal material in soil. Ranges from large undecomposed material to fine, highly decomposed material.
- Organic matter content of soil - Highly decomposed material we call humus. This is last stage of decomposition and it is a colliodal complex of materials that is resistant to further decomposition.
- Composition
- Green tissue - 85 to 90% water and 10 to 15% dry matter.
- Dry Matter
- C, H. and O - 90%.
- All nutrients but important reservoir of N, P, K, S.
- Rapidly decomposing materials - cellulose, starches, sugars, amino acids and proteins.
- Slowly decomposing materials - fats, oils, resins, and lignin.
- C, H. and O - 90%.
- Decomposition
- Due to enzymatic reactions of many different soil microrganisms. An oxidation reaction similar to burning.
CH2O + O2 ++> CO2 + CH2O + energy. - All stages of decomposition are present in soils.
- Decomposition process - microorganisms feed on organic matter to attain nutrients.
- Assume soil is low in fresh organic matter.
- Find low microorganism population and activity.
- Incorporate fresh plant material.
- Microorganism population multiplies many-fold.
- Tremendous evolution of CO2 and heat.
- Many of the nutrients in organic matter are incorporated into microbial tissue initially.
- As energy source diminishes, microbial activity lessens and microbes die, decompose, and some of the nutrients are released. Return to low microbial population and activity.
- Result - conversion of organic material to humus with release of nutrients and energy.
- Microorganism population multiplies many-fold.
- Assume soil is low in fresh organic matter.
- Due to enzymatic reactions of many different soil microrganisms. An oxidation reaction similar to burning.
- Green tissue - 85 to 90% water and 10 to 15% dry matter.
- Definition: living or dead plant or animal material in soil. Ranges from large undecomposed material to fine, highly decomposed material.
- VI. Soil Microorganisms - bacteria, fungi, atinomycetes, etc.
- Some decompose organic material, others responsible for other beneficial processes.
- Kinds and populations - affected by same things that affect plant growth: aeration, moisture, temperature, food supply, pH(p.157).
- Beneficial Reactions
- Ammonification - breakdown of organic matter and release of N as NH4+ .
- R-NH2 + H2O --> R-OH + NH3 + energy
NH3 + H2O --> NH4+ + OH-. - All plant nutrients are present in organic matter, and it is a particularly important reservoir of N, P, K, S.
- Ammonification is enhanced by well-drained, high base status soils.
- Fate of released NH4+
- Used by microrganisms.
- Plant uptake..
- Remain on exchange complex or fixed by illite.
- Undergoes conversion to NO3-.
- Used by microrganisms.
- R-NH2 + H2O --> R-OH + NH3 + energy
- Nitrification - conversion of NH4+ to NO3- by two special purpose bacteria.
- Two-step process
2 NH4+ + O2 --> 2 NO2- + 2 H2O + 4 H+ + energy
2NO2- + O2 --> 2 NO3- + energy- Second reaction is usually rapid and NO2- although very toxic, is seldom a problem.
- Acid forming process. Reason organic matter decomposition and NH4- containing fertilizers are acid forming.
- Second reaction is usually rapid and NO2- although very toxic, is seldom a problem.
- Responds to aeration, good moisture, 80 to 90 F temperature, high base status soil, and supply of NH4+.
- Two-step process
- Nonsymbiotic N fixation - accomplished by free-living organisms (Azotobacter, blue-green algae) that need only organic matter and O2.
- If N content of organic residues is low and insufficient, these organisms can remove N from air to meet their needs.
- When they die, N is released and can be used by plants.
- Fix 10 to 20 lb N/acre/year.
- If N content of organic residues is low and insufficient, these organisms can remove N from air to meet their needs.
- Symbiotic N fixation - accomplished by Rhizobium bacteria in association with legumes.
- Live in root infections called nodules.
- Obtain energy from host plant. Obtain N from air and fix enough for themselves and the host plant.
- Amount N fixed depends on how much is in the soil - high soil N. low N fixation.
- Respond to aeration, good moisture, 80 to 90 F temperature, high base status soil (pH 6 to 6.5), and supply of NH4+.
- Alfalfa - 250 lb N/acre/year. Soybean - 100 lb N/acre/year. Field pea - 50 lb N/acre/year.
- Live in root infections called nodules.
- Ammonification - breakdown of organic matter and release of N as NH4+ .
- Some decompose organic material, others responsible for other beneficial processes.
- Relation of C/N ratio in organic materials to decomposition and soil N.
- High ratio (> 30) - material low in N so microbes lack N and decomposition is slow. If any soil N is present in the soil, microbes will compete with plants for it.
- Have to apply additional N to hasten decomposition of high C/N material and prevent N deficiency on crop.
- Intermediate ratio (15 to 30) - balanced N content. Meets microbes needs and does not cause N deficiency.
- Low ratio (< 15) - contains excess N. N will be released into the soil with decomposition. Basis for legumes in rotations or green manure crops.
- High ratio (> 30) - material low in N so microbes lack N and decomposition is slow. If any soil N is present in the soil, microbes will compete with plants for it.
- Organic matter management
- Try to conserve in soil. Increases structure, water infiltration, CEC, and filth.
- Use soil for waste management - take advantage of decomposition for waste disposal.
- Convert it to stable organic residues and nutrients.
- Use plants to remove nutrients.
- Can lead to nutrient toxicities (Cd, Ni, Cu. Zn) and pollution of ground water by leaching (N) or erosion (N, P).
- Try to conserve in soil. Increases structure, water infiltration, CEC, and filth.
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Soil Organisms and Organic Matter
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