Agriculture 51 Principles of Soil Science Chapter 5 PDF

AGRICULTURE 51 Principles of Soil Science Chapter 5 Soil Organisms Brain Wash: COFFEE Brain Wash: Health and Coffee Brain Wash: Hamburger  Soil Organisms Soil organisms – creatures that spend all/part of their lives in the soil environment. Diversity of Soil Organism...

AGRICULTURE 51 Principles of Soil Science Chapter 5 Soil Organisms Brain Wash: COFFEE Brain Wash: Health and Coffee Brain Wash: Hamburger  Soil Organisms Soil organisms – creatures that spend all/part of their lives in the soil environment. Diversity of Soil Organisms Size of Organisms Macrofauna – Moles, mice, ants, beetles, termites, grubs, millipedes, earthworms, Mesofauna – Springtails and mites Microfauna – Nematodes and single- celled protozoans Flora – Plant roots, algae, diatoms Microorganisms – Fungi, bacteria, and actinomycetes  Types of Diversity Species Diversity – the mix of species present. Functional Diversity – the capacity to use a wide variety of substrates and provide a range of ecosystem services.  Ecosystem Dynamics Functional Redundancy – several organisms can carry out each ecosystem service. – leads to ecosystem stability and resilience Keystone Species – a species that is unique in filling an ecological niche and is therefore integral to the functioning of that system. Global Biodiversity – great genetic resource of soil organisms.  Stability & Resilience Stability – the ability of soils, even in the face of wide variations in environmental conditions and inputs, to continue to perform such functions as: – cycling of nutrients – assimilation of organic wastes – maintenance of soil structure Resilience – the ability of the soil to bounce back to functional health after a severe disturbance has disrupted normal processes. Organisms in the food web Autotrophs Organisms that can feed themselves by harnessing light energy to make organic molecules such as carbohydrates, proteins, lipids, and nucleic acids out of inorganic raw materials (such as CO2, H2O, N compounds, etc.) – Autotrophs = Primary Producers, the first link in the food web/chain.  Organisms in the food web Heterotrophs Organisms capable of deriving energy for life processes only from the decomposition of organic compounds and incapable of using inorganic compounds as sole sources of energy or for organic synthesis.  Soil Food Web The community of organisms living all/part of their lives in the soil. Fueled by primary producers: – plants, lichens, moss, photosynthetic bacteria, and algae.  Photosynthesizers First trophic level Algae Bacteria Role: – Capture solar energy to fix CO2 – Add OM to soil  Decomposers Second trophic level Bacteria Fungi Protozoa Role: – Breakdown residue – Immobilize nutrients in their biomass – Create new organic compounds – Bind soil aggregates  Mutualists Second trophic level vTwo organisms living in beneficial association Bacteria Fungi Role: – Enhance plant growth – Fix N  Symbiosis with Mycorrhiza Facilitates the uptake of P, other nutrients, and water uptake. Glomus spp. Acaulospora, P. tinctorius, etc.  Biological Nitrogen Fixation (BNF) the process by which microorganisms in the soil 'fix' atmospheric N and make it available for assimilation by plants. Nitrogen-fixing bacteria are Rhizobium, Azospirillum, etc.  Pathogens/Parasites Second trophic level Bacteria Fungi Nematodes Arthropods Role: – Promote disease – Consume roots – Parasitize nematodes or insects  Root-feeders Second trophic level Nematodes Arthropods Role: – Consume plant roots – Crop yield losses  Shredders Third trophic level Earthworms Arthropods Role: – Breakdown residue – Enhance soil structure – Provide habitat for bacteria in gut  Organism Abundance Soil organism numbers are influenced primarily by amount and quality of food available. Other factors include: – Physical factors = Moisture, temperature – Biotic factors = Predation and competition – Chemical characteristics of soil = Acidity, dissolved nutrients, and salinity  Food Web Structures Fungi to bacteria ratios – Grasslands/Ag soils 1:1 – Deciduous 5:1 to 10:1 – Conifer 100:1 to 1000:1 Organism communities reflect their food source Management practices change food webs How Soil Organisms Affect Soil Properties 1. Earthworms Digest organic and mineral matter passing their bodies - 30 tons/ha/year. Excreta/cast has high amounts of nutrients; high pH, % base saturation, and CEC. Through their passage in the soil, channels are created - facilitate aeration and drainage. Increases size and stability of soil aggregates. How Soil Organisms Affect Soil Properties 2. Nematodes Help in the decomposition of OM; – known as harmful parasites they invade plant roots and cause the death of the roots 3. Protozoa They ingest other soil organisms, particularly bacteria. – help hasten the release of some nutrients that have been immobilized by bacteria. How Soil Organisms Affect Soil Properties? 4. Bacteria Involved in OM decomposition as well as in various transformations of soil nutrients such as: – ammonification: organic N à NH3 – nitrification: NH4+ à NO3- – denitrification: NO3- à N2 – immobilization of N: available à unavailable form – biological N fixation: N2 to NH3 in root nodules – sulfur oxidation and reduction other chemical processes How Soil Organisms Affect Soil Properties? 5. Fungi The most adaptable and versatile of soil organisms. Able to thrive even in extreme soil acidity and alkalinity. Able to decompose even the resistant organic compounds such as lignins, cellulose, and gums. Mycorrhizae - help plants in solubilization of P and its absorption. How Soil Organisms Affect Soil Properties? 6. Actinomycetes These organisms also attack and simplify complex and resistant organic compounds such as: – cellulose – chitin – phospholipids  Autotrophic & Heterotrophic Bacteria Autotrophic bacteria – use CO2 as their source of C and derive energy for their metabolism from the oxidation of simple inorganic compounds such as: – Ammonium = NH4+ – Sulfur = H2S – Fe = Fe2+ Heterotrophic bacteria – oxidize organic matter to get C and energy.  Chemoautotrophic & Photoautotrophic Bacteria Chemoautotrophic – use inorganic chemical compounds. Photoautotrophic – use sunlight as their source of energy.  Aerobic, Anaerobic, & Facultative Bacteria Aerobic bacteria – thrive only in the presence of free oxygen. Anaerobic bacteria – can live even in complete absence of oxygen. Facultative bacteria – can grow in the presence/absence of free oxygen. – can use oxidized compounds such as nitrates and sulfates as electron acceptors. – in the process of reduction, NO3- is transformed to N2 or N2O and SO4= to H2S.  Mesophilic, Thermophilic, & Psychrophilic Bacteria Mesophilic: 25oC– 35oC Thermophilic: 45oC– 65 oC Psycrophilic: