NRES 201 Lecture 31 Outline of Last Lecture I The diversity of soil organisms II The food web III Organism abundance and metabolic activity Outline of Current Lecture IV Earthworms V Ants VI Termites VII Nematodes VIII Protozoa Current Lecture Earthworms The most important member of the soil micro fauna and the most beneficial for plant growth 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 fertility Soil and Environmental effects Burrows o Earthworms annually ingest 20 400 tons of soil per acre o Their burrows can be extensive particularly in the absence of tillage o Their burrows become channels for root growth Casts o Earthworm waste in the form of soil globules o 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 effects o Residue Incorporation Nearly eliminates thatch in turfgrass Helps conserve nutrients These 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 effects o Exposure of surface soil nightcrawlers can increase erosion by leaving more than half the soil bare o Stimulation of nutrient cycling invading nightcrawlers have depleted the O horizon in boreal forests o Promotion of macropore leaching Vertical earthworm burrows can serve as a pathway for chemical transport to tile lines but absorption is increased by the organic lining in these burrows Factors affecting earthworm activity o Activity favored by Moist well aerated soils well supplied with organic residues or surface mulch Cool soil temperature in the spring or fall A good supply of soil Ca at pH 5 5 8 5 o Activity is depressed by Moles mice and other predators Sandy soils Excess salinity Ammoniacal fertilization Insecticide application Tillage Ants 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 infiltration o Nests also stimulate soil N cycling with the influx of organic substrates that support 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 processes o Residues removed from most of the soil surface o Mount material is mainly from the subsoil so fertility is limited unless the subsoil exceeds 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 behavior o Sometimes attack plant roots Protozoa Single celled animals that include o Amoebas move by extending and contracting pseudopodia o Ciliates move by waving hair like projections o 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 scarce
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