Benefits of Soil Organisms. What kinds of plants and animals live in the soil?. 1) Bacteria: most numerous and important single celled plants, can reproduce in 20-30 minutes and may decrease rapidly in in favorable conditions
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What kinds of plants and animals live in the soil? 1) Bacteria: most numerous and important • single celled plants, can reproduce in 20-30 minutes and may decrease rapidly in in favorable conditions • a soil which has 5% O.M. can have 3 1/2 tons of bacteria per acre (ability to multiply quickly) • crops require free oxygen or aerated conditions in the soil • anaerobic bacteria (do not need free oxygen) get their oxygen from chemical reactions
What kinds of plants and animals live in the soil? 2) Actinomycetes: the size of bacteria, but some resemble molds • can live under drier conditions than bacteria, abundant in sod • among the most important agents of the soil in the breakdown of dead plant materials, including cellulose • responsible for characteristic smell of freshly tilled soil • Can produce useful antibiotics (streptomycin, terramycin, neomycin)
What kinds of plants and animals live in the soil? • 3) Fungi: most are too small to be seen by the naked eye, except for yeast, molds, mushrooms, puffballs, and toadstools • fungi do not have chlorophyll and must get their food from organic substances • Type of organic matter in soil determines type of fungi that will prevail • Secrete substances that aid in the formation of soil aggregates • Continue the decomposition process after bacteria & actinomycetes have ceased to function
What kinds of plants and animals live in the soil? • 4) Algae: contain chlorophyll • ex: seaweed, scum-forming algae on ponds • soil algae are too small to be seen with the naked eye, but in large numbers can give soil surface a green color • favor damp soil that is exposed to the sun • believed to be able to fix free nitrogen from the air in the soil, valuable to rice production • Some symbiotic algae associate with one of several fungi in forms called “lichens” (help weather rock surfaces)
What kinds of plants and animals live in the soil? • 5) Protozoa: minute animals found in the soil, smallest form of animal life • must live in a water film
What purpose do microorganisms have? • decay plant residue (straw etc.) • make free nitrogen in the air available to plants • break down nutrients needed by plants • break down cellulose • much of the food in the soil is not available to the plant, until microbes break them down
What is Nitrogen Fixation? • the process of changing free nitrogen from the air into plant useable nitrogen by bacteria • two types of nitrogen fixing bacteria: • 1) attached to the roots of legumes • 2) live freely in soil (few) • a column of air 1" square weighs 14.7 pounds. Our atmosphere is about 75% nitrogen. How many pounds of nitrogen are in the air above one acre?
How much Nitrogen is in the Air above one acre? There are 69,155,856 pounds of nitrogen in the air above an acre.
How do Nitrogen Fixing nodules form? • bacteria enter the single-celled root hairs where they multiply rapidly due to favorable conditions, the colonies then form into nodules, usually in bunches
What are false nodules? • insects may injure legumes causing false nodules
What is Inoculation? • when a legume plant is grown for the first time, it is essential to expose the seed to Rhizobium bacteria (nitrogen fixing) before planting
How much nitrogen is added to the soil by bacteria? • free soil bacteria add 10-50 lbs./yr. • nodule bacteria add 50-100 lbs./yr. • may not be a net gain due to nitrogen in harvested crop • gene splicing may yield a corn plant with nitrogen fixing qualities. This would save the producer money and reduce the need for petroleum (most commercial fertilizers are made from petroleum)
What are some of the harmful effects of soil microorganisms? • bacterial diseases: potato and tomato wilt, mildews, blights, dry rot • microbes compete for food with the crop, it there are any shortages of nutrients this could harm the plant • nitrogen tie-up
What are favorable conditions for soil microorganisms? • food, temperature, moisture, acidity, and aeration: most are similar to plants • most are injured by direct sunlight except algae (chlorophyll)
What problems result from soil management practices? • conservation tillage reduces microbe activity, thus fertilizer must be added to feed the microbes and speed decomposition (add 20# N/ton of straw)
Why do producers summer fallow? • conserve water • conserve nitrogen
What are some of the higher forms of animal life in the soil? • slugs & snails: feed on the surface, favor damp shady conditions • arthropods: insects (ants, centipedes) most feed on decaying O.M. • nematodes: (microscopic, unsegmented worms) abundant in soils, three groups: • 1) feed on plants • 2) feed on other life forms • Earthworms - feed on decaying O.M. (earthworms) up to 500 lbs per acre, aerate soil, allow water to penetrate, excrement is good plant food
What are some of the higher forms of animal life in the soil? • rodents, gophers, squirrels, prairie dogs: most are considered a nuisance. Burrows are similar to those of worms, but can be a menace
How to plant roots benefit the soil organisms? • plant roots hold down surface soil • break up subsoil • provide O.M. • add minerals, air, and water • channels for air & water penetration • loosen soil