Thursday’s Quiz will Cover:• Intro to soil lecture (last Thursday)• Soil Article (last Thursday)• Chapter 9 Reading Guide and Soil Topography

Questions (Last Friday)• Soil Organisms (Decomposers) Lecture (Today)• Vermiculture Reading Questions (Today)____________________________________Side note: Final will cover soil lab and tomorrow’s

lecture and Friday’s webquest as well.

1

What kinds of plants and animals live in the soil?

1) Bacteria: most numerous and important– can reproduce in 20-30 minutes and may decrease

rapidly in unfavorable conditions– a soil which has 5% O.M. can have 3 1/2 tons of

bacteria per acre (ability to multiply quickly)– anaerobic bacteria (do not need free oxygen) get

their oxygen from chemical reactions

2

What kinds of plants and animals live in the soil?

2) Actinomycetes: type of bacteria, but some resemble molds– can live under drier conditions than

other 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

3

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 – glomalin or “soil glue”– Continue the decomposition process after

bacteria & actinomycetes have ceased to function4

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)

5

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

6

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

7

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 root nodules of legumes– 2) live freely in soil (rare)

8

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

9

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)

10

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, if there are any shortages of nutrients this could harm the plant

11

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)

12

What best management practices (BMPs) can help soil biota?

• Conservation Tillage-increased soil stratification and size and activity of soil organism populations under conservation tillage compared to conventional tillage leads to increased nutrient retention.

• Crop Rotation-increases microbial diversity

13

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

14

What are some of the higher forms of animal life in the soil?

• Earthworms– Feed on decaying O.M. (earthworms) up to 500

lbs per acre, aerate soil, allow water to penetrate, excrement is good plant food

15

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

16

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

17

EXIT SLIP1 Name 5 types of microorganisms present in

soil?2 What functions do soil microorganisms

perform?3 What is nitrogen fixation?4 Where does the majority of nitrogen get

fixed?5 What BMPs help soil organisms? How?

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