Soil Ecology: Organisms, Environmental Factors, and Clay Minerals
Soil Ecology: Organisms and Their Roles
Nature Activities and Role in Metabolic Energy Transformation Processes
Environmental Parameter Relations
Relationships between microbial activity measured by the respiratory activity of soil CO2 flux.
Microfauna
- Protozoa
- Nematodes
Microflora
- Actinomycetes
- Fungi
- Soil Algae
Monera (Prokaryotes)
- Bacteria:
- Streptomyces
- Pseudomonas
- Nitrobacter
- Nitrosomonas
- Anaerobic:
- Clostridium
- Aerobic Actinomycetes:
- Streptomyces
- Bacteria to hyphae – Nocardia (degrade humic substances)
Cyanobacteria
- Nostoc
- Anabaena
Synthesize vitamins
Protists
- Protozoa and microphages (mainly saprophytes, feeding on bacteria)
- Amoeba: Degrade lignin
- Flagellates: Bodo – Oikomonas
- Amoebae
- Ciliates: Colpodo, Vorticella
Some Aerobic Fungi
Break down lignin, heterotrophs
- Ascomycetes: Penicillium, Aspergillus, Morchella
- Basidiomycetes
Plant Soil
- Chlorophytes (green algae)
Animals
- Worms: Nematodes (pseudocoelomate), seudocelomados (0.5 to 1.5 mm long), cylindrical (cuticles)
- Phytoparasitic: Meloidogyne
- Fungivores
- Bacterivores
- Omnivores: Have a digestive tube
Coelomates
Worms and body cavity (coelom). The circulatory system has a gut. Hermaphroditic freshwater annelid.
Earthworms
Present glandular cells, ingest soil mass. Secrete CaCO3 in the esophagus. Excrete ammonia and N-Urea NH4. Eisenia foetida. Redox potential (Eh) = -180 to 460.
Organism Classification
Class 1
A: Autotrophs: Obtain energy from sunlight, CO2 fixed by photosynthesis (algae, bacteria, higher plants).
B: Chemolithotrophs: Obtain energy from chemical reactions, organic C and CO2 fixation (Nitrosomonas, Nitrobacter, Desulfovibrio desulfuricans).
C: Heterotrophs: Use organic compounds for energy and carbon source, recycle organic compounds (fungi, bacteria, animals).
D: Symbionts: Obtain energy and nutrients from plants (N-fixing bacteria, mycorrhizal fungi).
Class 2: Bodies
- Macrofauna: Size (6 to 200 mm), vertebrates
- Mesofauna: Size (200 to 6000 mm), arthropods, annelids, mollusks
- Microorganisms: Size (<200 mm), nematodes
Soil Colloids and Clay Minerals
Colloids
- Organic: Fraction of humified organic matter
- Inorganic: Silicate clays, crystalline gels of Al and SiO2, oxides and hydroxides of Fe and Al
Clay Fraction
Particles less than 2 µm, found as primary minerals or larger size as kaolinite.
Crystalline Clays
The crystals are composed of a number of individual layers superimposed. Two basic structural units: Tetrahedron (silicon atom in the center) and octahedron (aluminum atoms). Must always be electrically neutral.
Isomorphic Substitution
Change in structure between ions that occur during the formation of clays. Rc / Ro.
Group 1: Kaolinite
Clay type 1:1, low cation exchange capacity (CEC), underdeveloped colloidal properties, little or no isomorphic substitution.
Group 2: Montmorillonite
Clay type 2:1, high CEC, highly developed colloidal properties, high isomorphic substitution.
Group 3: Hydrated Micas (Illite)
Clay type 2:1, intermediate properties, less isomorphic substitution.
Group 4: Chlorite
Clay type 2:2, interlayer structure with aluminum. Low in Chilean soils.
Group 5: Vermiculite
Clay type 2:1, high capacity for K+ retention.
Origin of Clays
- Inheritance: Clays are part of the parent material, typical of sedimentary soils.
- Transformations: Limited changes in the primary minerals, constituents are lost by degradation.
- Neoformation: Significant change with the rupture of primary minerals and reconstitution of other minerals, according to new equilibrium conditions.
Conditions for the Formation of Different Clay Minerals
- Montmorillonite
- Vermiculite
- Illite
- Kaolinite
- Halloysite
- Allofan
- Gibbsite