Organic Matter

Question 1

What is organic matter?

Answer 1

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

Question 2

What is organic matter

Answer 2

Living organisms <10%

Stabilized organic matter (humus) 33%-50%

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

Question 3

Living Organisms

Answer 3

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

Question 4

Dead plant material; organic material; detritus; surface residue

Answer 4

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

Question 5

Detritivores

Answer 5

organisms that feed on such material

Question 6

Active fraction organic matter

Answer 6

organic compounds that can be used as food by microorganisms.

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

Question 7

Labile Organic matter

Answer 7

organic matter that is easily decomposed

Question 8

Root exudates

Answer 8

soluble sugars, amino acids and other compounds secreted by roots

Question 9

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

Answer 9

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)

Question 10

Lignin

Answer 10

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

Question 11

Recalcitrant organic matter

Answer 11

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

Question 12

Humus or humified organic matter

Answer 12

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

Question 13

Humus

Answer 13

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

Question 14

Bacteria

Answer 14

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

Question 15

Actinomycetes

Answer 15

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

Question 16

Fungi

Answer 16

Dominate in forest soils

Aerobic

Different roles for different species: Mycorrhizae, Decomposers, Pathogenic

Hyphae, mycelia

Question 17

Protozoa

Answer 17

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

Question 18

Nematodes

Answer 18

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

Question 19

Arthropods

Answer 19

many that influence soil in many ways

Question 20

Earthworms

Answer 20

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

Question 21

Earthworms

Answer 21

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

Question 22

Types of Earthworms

Answer 22

Epigeic: Surface and soil litter

Endogeic: upper soil species

Anecic: deep-burrowing species

Question 23

What does organic matter do?

Answer 23

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

Question 24

compaction

Answer 24

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

Question 25

Surface Crusting

Answer 25

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

Question 26

Organic material is not organic matter

Answer 26

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

Question 27

What is the difference between organic material and OM

Answer 27

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

Question 28

Decomposition

Answer 28

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

Question 29

Organic Material is unstable in soil

Answer 29

changes from mass readily as decomposition takes place as much as 90 % disappears as a result of decomposition

Question 30

Organic matter (OM)

Answer 30

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

Question 31

How much OM is in the soil?

Answer 31

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

Question 32

How much OM is in soil

Answer 32

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

Question 33

How much OM soil

Answer 33

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

Question 34

Benefits of OM

Answer 34

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

Question 35

Available Phosphate

Answer 35

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)

Question 36

Benefits of OM

Answer 36

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

Question 37

Benefits of OM

Answer 37

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

Question 38

Benefits of OM

Answer 38

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

Question 39

Management practices to maintain OM in soils

Answer 39

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)