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THE LIVING, THE DEADAND

THE VERY DEAD

The Role of Soil Organic Matter in the N Cycle

SOIL FORMING PROCESSES LIVING ORGANISMS

• Soil differences related to difference in plant growth over time

• Macroscopic

• Microscopic

• Human

BIOLOGICAL SOIL PROPERTIES

“Soil Organic matter….

The living…The dead….

And the very dead”.

Fred Magdoff

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• Bacteria

• Fungi

• Protozoa

• Nematodes

• Arthropods

• Algae

• Plant roots

• Earthworms, and other larger animals

O.M. represents about 15% of the total soil organic matter.

O.M. represents about 15% of the total soil organic matter.

SOIL ORGANIC MATTERTHE LIVING

SOIL ORGANIC MATTERTHE DEAD

• Crop residue

• Green manure

• Livestock manure

• Sewage sludge

Source of carbon and nutrition for soil microbes.Source of carbon and nutrition for soil microbes.

SOIL ORGANIC MATTERTHE VERY DEAD

Humus

• A product of plant and animal remains.

• More complex than organic matter

• More difficult for other organisms to breakdown.

• Humus can last for many years in the soil.

The “Good Stuff” that makes-up our fertile soils.

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TEMPORARY N LOSSImmobilization-Mineralization

Time

Plant-available

“+” Change

Activity of microorganisms

Add sawdust C:N = 500:1

NITRATES

MICROBES

Sawdust totally degraded

C:N ratio and direction of reaction

• C:N ratios of 20:1 or less (Mineralization)

• C:N ratios of 30:1 or more (Immobilization)

• C:N ratios of 20:1 to 30:1 (No net change)

SOIL ORGANIC MATTERCARBON-to-NITROGEN RATIO (C:N)

OUR C:N Ratio 18/3 = 6:1

SOIL ORGANIC MATTERHUMUS

Stable Organic MatterC:N Ratio = 10:1

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COMMON C:N RATIOS

GREEN MATERIAL C:N Ratio BROWN MATERIAL C:N RatioAged Chicken Manure 7:1 Leaves 70:1Food Scraps 17:1 Straw/Hay 90:1Coffee grounds 25:1 Wood chips 700:1Grass clippings (fresh) 25:1 Shredded newspaper 175:1Fresh weeds 20:1 Nut Shells 35:1Fruit waste 30:1 Pine Needles 80:1Rotted manure 20:1 Corn Stalks 60:1Seaweed 19:1 Wheat Straw 60:1General garden waste 30:1

Maintaining Soil O.M.

100%

50%

Begin permanent sod

25 years after tillage began

Tillage begins

Time

SOIL ORGANIC MATTERMINIMIZING LOSS

• Minimize tillage

• Add residues/green manure

• Maintain environment for good microbes

• Control soil erosion

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7.MINERALIZATION

6.4.

NITRIFICATION5.

1.

FIXATION

Plant Uptake

DENITRIFICATION

VOLATILIZATION

LEACHING

IMMOBILIZATION

7.MINERALIZATION

6.4.

NITRIFICATION5.

1.

FIXATION

DENITRIFICATIONIMMOBILIZATION

LECTURE 4 ASSIGNMENT

• Watch this short Youtube video and offer a comment about what you see.

https://www.youtube.com/watch?v=Mxp1nnrUG0Q

Bioturbation: The reworking of soils and sediments by animals or plants.

Soil Fauna: the organisms of the soil considered as a whole.

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ADDITONAL READING

• Building Soils for Better Crops is a one-of-a-kind, practical guide to ecological soil management, now expanded and in full color. It provides step-by-step information on soil-improving practices as well as in-depth background—from what soil is to the importance of organic matter. A must-read for farmers, educators and students alike.

http://www.sare.org/Learning-Center/Books/Building-Soils-for-Better-Crops-3rd-Edition