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Soil Fertility > Organic Matter > Flashcards

Organic Matter Flashcards

1
Q

What is organic matter?

A

Consists of plant and animal residues at various stages of decomposition, cells and tissues of soil organisms and substances synthesized by soil organisms

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2
Q

What is organic matter

A

Living organisms <10%

Stabilized organic matter (humus) 33%-50%

Decomposing organic matter (active fraction) 33%-50%

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3
Q

Living Organisms

A

bacteria, fungi, nematodes, protozoa, earthworms, arthropods and living roots

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4
Q

Dead plant material; organic material; detritus; surface residue

A

refer to plant or other organic substances that have recently been added to the soil and have only begun to show signs of decay

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5
Q

Detritivores

A

organisms that feed on such material

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6
Q

Active fraction organic matter

A

organic compounds that can be used as food by microorganisms.

The active fraction changes more quickly than total OM in response to management changes

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7
Q

Labile Organic matter

A

organic matter that is easily decomposed

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8
Q

Root exudates

A

soluble sugars, amino acids and other compounds secreted by roots

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9
Q

Particulate organic matter (POM) or light fraction (LF) organic matter

A

POM and LF have precise size and weight definitions.

Thought to represent the active fraction of OM which is more difficult to define.

Larger and lighter than other types of soil OM (can be separated using a sieve)

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10
Q

Lignin

A

A hard to degrade compound that is part of the fibers of older plants. Fungi can use the carbon ring structures in lignin as energy source

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11
Q

Recalcitrant organic matter

A

OM such as humus or lignin containing material that few soil organisms can decompose

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12
Q

Humus or humified organic matter

A

stable long lasting remnant of decaying OM (a complex, dark-brown, amorphous-heterogeneous [non-crystalline, non-uniform] structure that no longer resembles the decaying matter of origin

Resistant to further microbial decay

has chemical and physical properties of great importance to soils and plants

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13
Q

Humus

A

not readily decomposed

physically protected inside of aggregates or chemically too complex to be used by most organisms

important in binding tiny soil aggreagates

improves water and nutrient holding capacity

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14
Q

Bacteria

A

100 million to 1 billion per gram

decomposition in turf soils and compost heaps

Rhizobia- N fixers

food for other members of the food web

Bacteria and their wastes have CEC

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15
Q

Actinomycetes

A

are a type of bacteria that look like fungi because they form hyhae

they decompose hard to decay substances like chitin and cellulose

White mycelia in dry compost heaps

earthy smell of soil comes from these

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16
Q

Fungi

A

Dominate in forest soils

Aerobic

Different roles for different species: Mycorrhizae, Decomposers, Pathogenic

Hyphae, mycelia

17
Q

Protozoa

A

Single-celled bacteria that feed primarily on bacteria, releasing N as ammonium (bacteria have a lower C:N that protozoa require, therefore excess N is excreted)

Need a water film to move in

1000 to 1 mill per teaspoon

18
Q

Nematodes

A

Non-segmented round worms

1mm length

Most are beneficial but some eat plant roots

Operate on several trophic levels: feed on plants and algae, feed on bacteria and fungi, feed on other nematodes

19
Q

Arthropods

A

many that influence soil in many ways

20
Q

Earthworms

A

Major decomposers; dramatically alter soil

Stimulate microbial activity through their cast (feces)

Mix aggregate soil

increase infiltration

improve water holding capacity (through aggregates)

bury and shred plant residue

21
Q

Earthworms

A

Derive their nutrition from fungi and bacteria

eaten by some flatworms and one species of parasitic fly

main predators are birds and mammals

Favored by low-till agriculture

22
Q

Types of Earthworms

A

Epigeic: Surface and soil litter

Endogeic: upper soil species

Anecic: deep-burrowing species

23
Q

What does organic matter do?

A

of the components…..OM is arguably the most important; also the most misunderstood

serves as a reservoir of nutrients and water

aids in reducing compaction and surface crusting

increases water infiltration

often ignored or neglected

24
Q

compaction

A

drier the soil less compaction, the wetter the soil the deeper compaction goes (But not really sig. different)

25
Q

Surface Crusting

A

tilling causes small particles, when it rains the small particles are moved and packed together and then dry into hard cement like layer

26
Q

Organic material is not organic matter

A

leaves, manure, or plants parts…..not OM

27
Q

What is the difference between organic material and OM

A

Organic material is anything that was alive and is now in or on the soil

will eventually become OM through decomposition

Needs to be converted by microorganisms to a resistant state of decomposition

28
Q

Decomposition

A

Organic materials to inorganic

biological process that includes physical breakdown and biochemical transformation of complex organic molecules of dead material into simpler organic and inorganic molecules

(C6H10O5)n + O + F&B –> CO2+ H2O + Heat

29
Q

Organic Material is unstable in soil

A

changes from mass readily as decomposition takes place

as much as 90 % disappears as a result of decomposition

30
Q

Organic matter (OM)

A

is stable (for the most part)

usually only ~5% of OM mineralizes each year

Rate increases based on temperature, oxygen, and moisture: occurs with excessive tillage, stable OM is analyzes in soil test

31
Q

How much OM is in the soil?

A

an acre of soil (6in depth) weighs ~2,000,000lbs

if we have ~1% OM weight=~20,000 lbs per acre: takes at least 10lbs of organic material to decompose into 1lb of OM, 100 tons of organic material applied or returned to soil to add 1% stable OM under favorable conditions

32
Q

How much OM is in soil

A

Soils formed under prairie vegetation are generally high in OM (top growth and roots)

ex. 1.4 tons of organic material per acre from shoot growth….4 tons acre from root yield

33
Q

How much OM soil

A

soils formed under forest vegetation usually have comparably low OM: trees produce a smaller root mass per acre than grass plants and trees are perennials

Much of the OM in a forest is tied up in the tree itself instead of being returned to the soils

Prairie soils have ~twice OM than forest derived soils

34
Q

Benefits of OM

A

Nutrient supply: OM is a reservoir of nutrients to be released to the soil, each % of OM in the soil releases ~20-30 lbs of N, ~4.5-6.6lbs of P2O5, and ~2-3lbs of sulfur per year

Nutrient release occurs primarily in spring/summer

35
Q

Available Phosphate

A

P2O5 equivalent of fertilizer soluble in water plus neutral ammonium citrate, and considered readily available to growing plants (however it is never found in fertilizer)

36
Q

Benefits of OM

A

Water holding capacity:

OM behaves like a sponge: can absorb and hold up to 90% of its weight in water

OM will release most of this water to plants

in contrast clay holds approx. same amount of water, but this is mostly unavailable to plants

37
Q

Benefits of OM

A

Soil structure aggregation:

OM causes soil to clump and for soil aggregates

improves soil structure, improved soil structure improves permeability which in turn improves the ability to take up and hold water

38
Q

Benefits of OM

A

Erosion prevention:

increases from 1-3% OM can reduce erosion 20-35% due to increased infiltration and stability of soil aggregates

39
Q

Management practices to maintain OM in soils

A

Reduce or eliminate tillage: tillage aerates the soil causing a flush of microbial activity. This speeds up the decomposition process. Increases erosion

addition of organic material

cover crops

field rotation (fallow)

Soil Fertility (4 decks)

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