© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Chapter 5 Life in the Soil

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Objectives After completing this chapter, you should be able to: –Define the carbon cycle and explain its importance –Describe the soil food web and explain its importance –Briefly describe soil organisms –List ways that soil organisms are important –Describe how to promote populations of beneficial soil organisms

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Teeming with Life One teaspoon of fertile soil could contain: –100 nematodes –250,000 algae –300,000 amoeba –450,000 fungi –11,700,000 actinomycetes –100,000,000 bacteria

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Important Soil Organisms 1.Earthworms 2.Nematodes 3.Algae 4.Fungi 5.Bacteria 6.Actinomycetes 7.Protozoa

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Beneficial Effects of Soil Organisms 1. Organic matter decomposition -- plant residues release nutrients for plant reuse -- bacteria, fungi and actinomycetes 2. Detoxify chemicals -- Break down pesticides, oil spills, etc. 3. Nitrogen ‘fixation’ 4. Nutrient transformations 5. Plant protection. - nematode-trapping fungi - antibiotic-producing actinomycetes

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. The Soil Food Chain and Carbon Cycle Food chain or food web –How food moves from one organism to the next –Operate above the ground and in the soil and interconnect –All organisms are part of some food chain –Base of most food chains, both above and in the soil, is photosynthesis by plants

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. The Soil Food Chain and Carbon Cycle (cont’d.) Food chain components –Primary producers and consumers –Secondary consumers –Detritus –Decomposers –Organic matter –Humus

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. The Soil Food Chain and Carbon Cycle (cont’d.) Roles of interest –Producers –Herbivores –Predators –Parasites –Saprophytes –Symbionts

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. The Soil Food Chain and Carbon Cycle (cont’d.) Microflora –Bacteria: one-celled organisms that lack a nucleus –Fungi: mass of tangled hyphae called mycelium –Actinomycetes: look like fungi but are bacteria –Algae: single-celled, plant-like organisms Microfauna –Protozoa: single-celled, animal-like organisms

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Distribution of Microorganisms Distribution of soil –Rhizosphere: area one to two millimeters from plant roots –Plants benefit from the concentration of microbes near the root systems Nutrient cycling –Mineralization: microorganisms in the rhizosphere break down nutrients in the organic pool so they can become part of the inorganic pool Immobilization is the opposite process

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Nitrogen Fixation Process of converting nitrogen gas to ammonium ions through a series of biological reactions –Ammonium ions can be utilized by plants Leguminous plants –Form associations with soil bacteria, which enhances the nitrogen fixation process

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Mineralization Nitrogen fixed by soil microbes is immobilized in bodies of microbes or host plants –When these die, they decay to form a pool of organic nitrogen Mineralization is a facet of decay –Conditions that promote decay promote mineralization

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Nitrification and Denitrification Nitrification –Oxidation process Strips hydrogen off the nitrogen atom, producing lots of hydrogen ions –Conditions that promote the activity of the nitrifying bacteria increase the rate of nitrification Denitrification –Completes the nitrogen cycle by converting nitrate ions to nitrogen gas Filters out of the soil

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Soil Aggregation and Plant Growth Promotion Soil aggregation –Soil microbes: important agents Plant growth promotion –Some interactions of plants and microorganisms attached to their roots or occupying the rhizosphere enhance plant health and vigor

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. An Important Fungus Mycorrhizae – “fungus root.” Fungi that form a symbiotic relationship with roots of plants. Increase the effective root surface area for absorbing water and nutrients (10X) Increase P uptake (also Zn, Cu, and Mo) Form protective “sheath” around root Reduce plant stress to drought, adverse pH, pathogens, low nutrition, and adverse temperatures First noted on tree species, now known to affect most plants species.

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Plant Growth Promoting Rhizobacteria Actively improve plant growth –May act by producing plant hormones and vitamins by improving nutrient uptake or suppressing root disease Microbes need organic matter –Food source

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Rhizobium Bacteria and Nitrogen Fixation 78% of atmosphere is N ,500 tons of nitrogen in air above each acre (but not usable). Average Rhizobium Fixation Rates: Alfalfa #N per acre per year Soybeans #N Peanuts and Beans #N

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. P N

Actinomycetes “mold bacteria” Resemble bacteria (similar cell structure); but also look life fungi because they are filamentous. Live on decaying organic matter Some species produce antibiotic compounds that kill other microbes - Actinomycin, Neomycin, Streptomycin The smell of freshly plowed ground comes from chemicals produced by actinomycetes

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Breaking Down Chemicals Bioremediation –Soil organisms can be used to remove toxins from contaminated environments Oil spills Pesticides Organic wastes

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Methane Production and Absorption Methanogenesis –Anaerobic organisms produce methane while breaking down organic matter in oxygen-free sites Methane –Also known as swamp-gas –Major component of natural gas fuel

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Managing Soil Organisms Biologic activity –Important indicator of soil quality Inoculation –Purposely infecting soils with useful organisms –Rhizobium inoculation has been a common practice for many years Improving soil conditions –Enhances natural populations of desirable soil micro- organism and makes the soil hospitable

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Managing Soil Organisms (cont’d.) Supplying organic matter –Sources: crop residue, outside sources, and cover crops Improving soil conditions –Reduce tillage, improve drainage, minimize compaction, reduce pesticide use, maintain adequate nutrient levels, minimize fallow, and keep soil covered Increasing habitat diversity –Rotate crops, cover crops, intercrop, and diversify the landscape

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Controlling Harmful Organisms Methods –Sterilization and solarization –Practice sanitation –Obey quarantines –Control soil pH –Rotate crops –Incorporate organic matter –Utilize plant residues and living pesticides –Use suppressive media in container growing

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Important Soil Organisms (cont.) 2. Nematodes Microscopic, unsegmented, thread-like worms (nema = threadlike). Swim about in the water-filled soil pores. When soil dries up, they enter a cryptobiotic resting state. Some species infect roots of crop plants ($2 billion annually).

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Tobacco Plant Infested With Root-knot Nematodes

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Soybean Cyst Nematode

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Fungi eating a nematode

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Soil Animals Groups –Macrofauna Function to mix and invert soil and create larger soil channels –Mesofauna Do the same as macrofauna but are also involved in the decay process by shredding organic matter and contributing to soil structure

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Soil Animals (cont’d.) Mesofauna –Nematodes –Arthropods Macrofauna –Earthworms –Mammals

© 2013 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Summary This chapter reviewed several topics –Soil life and the food chain –Microorganisms –Nutrient cycling –Nitrogen –Interactions in the rhizosphere –Common soil mesofauna and macrofauna –Soil quality indicators