NRES 201 Lecture 31 Outline of Last Lecture I. The diversity of soil organismsII. The food webIII. Organism abundance and metabolic activityOutline of Current Lecture IV. EarthwormsV. AntsVI. TermitesVII. NematodesVIII. ProtozoaCurrent LectureEarthworms - - The most important member of the soil micro fauna and the most beneficial for plantgrowth- Known as nature's tillers because their burrowing actions loosen the soil- They eat their way through the soil - Bacteria are their main food- Their manure improves soil fertilitySoil and Environmental effects - - Burrowso Earthworms annually ingest 20 - 400 tons of soil per acreo Their burrows can be extensive particularly in the absence of tillageo Their burrows become channels for root growth- Castso Earthworm waste in the form of soil globuleso These globules: Are often deposited on the soil surface Consist of a mixture of organic and mineral matter Occur as stabilized aggregates Have a high content of nutrients and CaCO3- Other beneficial effectso Residue Incorporation: Nearly eliminates thatch in turfgrass Helps conserve nutrientsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Earthworm burrows reduce soil compaction and increase water infiltration,aeration, and drainage. - Deleterious effectso Exposure of surface soil - nightcrawlers can increase erosion by leaving morethan half the soil bare o Stimulation of nutrient cycling - invading nightcrawlers have depleted the Ohorizon in boreal forestso Promotion of macropore leaching - Vertical earthworm burrows can serve as apathway for chemical transport to tile lines but absorption is increased by theorganic lining in these burrows. - Factors affecting earthworm activity - o Activity favored by: Moist, well aerated soils well supplied with organic residues or surfacemulch Cool soil temperature in the spring or fall A good supply of soil Ca at pH 5.5 - 8.5o Activity is depressed by: Moles, mice and other predators Sandy soils Excess salinity Ammoniacal fertilization Insecticide application TillageAnts - - Nearly 9000 species inhibit the soil - the majority occur in the humid tropics- Effects on the soil ecosystem - o Nest - building by ants can improve soil aeration and water infiltrationo Nests also stimulate soil N cycling with the influx of organic substrates thatsupport an active microbial population. o Ants can adversely affect plant growth by raising aphids that suck plant sap. Termites - - About 2000 species worldwide- Most prominent in tropical and subtropical areas- Main food is cellulose from grasses, wood houses, etc- Digestion is by anaerobic bacteria and protozoa in the gut which also produces methane- They live in colonies- Effect on soil productivity - o Much less beneficial than earthworms due to more efficient digestive processeso Residues removed from most of the soil surfaceo Mount material is mainly from the subsoil so fertility is limited unless the subsoilexceeds the topsoil in nutrient supply, clay content, or in drainage. Nematodes - - Unsegmented roundworms that occur in almost all soils- Require at least some moisture- Predatory behavior - Parasitic behavioro Sometimes attack plant rootsProtozoa - - Single - celled animals that include:o Amoebas - move by extending and contracting pseudopodiao Ciliates - move by waving hair-like projectionso Flagellates - move by waving a whip-like flagellum- Prey upon bacteria- Prefer moist, well drained soils and are most active around plant roots- Form cysts in dry soils or when food is
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