Organic Matter

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Organic Matter The key to healthy soils Fred
Magdoff Dept. of Plant Soil Science University
of Vermont
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Characteristics of Healthy Soils

• Sufficient (but not excess) nutrients
• Good tilth
• Sufficient depth
• Good water storage and drainage
• Free of chemicals that might harm plants

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Characteristics of Healthy Soils

• Low populations of plant disease and parasitic
  organisms
• High populations of organisms that help plant
  growth
• Low weed pressure
• Resistance to being degraded
• Resilience

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• There are three general types of organic
  matter in soils
• Living
• Dead
• Very Dead

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plant roots
bacteria
nematodes
Living
fungi
earthworms
mites
springtails
moles
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Dead Recently dead soil organisms and crop
residues provide the food (energy and nutrients)
for soil organisms to live and function. Also
called active or particulate organic matter.
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Very Dead Well decomposed organic
materials, also called humus. Humus contains very
high amounts of negative charge.
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All three types of soil organic matter play
important roles in helping produce high yields of
healthy crops.
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Soil organic matter
living 10-20
Organic matter is 1-6 of total soil mass
active (dead) 10-20
humus (very dead) 60-80
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Organic Matter Influences a Vast Number of
Important Soil Properties
For Example

• Nutrient availability
• Aggregation (and infiltration and drainage)
• Water storage
• Diversity and activity of soil organisms
• Soil color
• Presence of growth stimulating compounds
• Important global cycles carbon, nitrogen, and
  water are strongly influenced by soil organic
  matter

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Nutrient Availability
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As organic matter is decomposed nutrients are
transformed into forms that are available to
plants.
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From 50 to close to 100 of the CEC is due to
soil organic matter
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Cation Exchange Capacity and Chelation
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Corn grown in nutrient solution with (right) and
without (left) humic acids. Photo by R.
Bartlett.
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Soil Tilth
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infiltration
runoff
a) aggregated soil
b) soil crusts after aggregates break down
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Root heavily infected with mycorrhizal
fungi (note round spores at the end of some
hyphae). Photo by Sara Wright.
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Add organic matter
Increased biological activity ( diversity)
Reduced soil-borne diseases, parasitic nematodes
Aggregation increased
Decomposition
Nutrients released
Pore structure improved
Humus and other growth promoting substances
Harmful substances detoxified
Improved tilth and water storage
HEALTHY PLANTS
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Building Healthy Soil
1. Add plentiful amounts of organic materials
crop residues (including cover crops) as well as
off-field sources such as animal manures and
composts.
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Water stable aggregates following addition of 1
dm basis of dairy manure compost, small grain
straw, grass clippings, or dairy manure.
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a
Average for three soils (sand, loam, and clay)
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Water stable aggregates 0.25 to 4 mm diameter as
a percent of total soil
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b
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b, c
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c
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c
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ch
comp.
str.
grass
manure
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Building Healthy Soils
2. Keep the soil covered with living vegetation
and/or crop residue.
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• Use cover crops or perennial sod cover routinely.
  
• Reduce tillage intensity.

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Building Healthy Soils
3. Use better crop rotations.
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• Grow perennials as well as annual crops
• Different rooting depths
• Different growth and harvest times
• Some high-residue crops
• Different crop families
• Etc.

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Building Healthy Soils
4. Reduce tillage intensity.
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• Many different reduced till systems
  conservation till, ridge till, no-till.
• Better planters help.
• Cover crops can help.

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Building Healthy Soils
5. Use other practices that reduce runoff and
erosion.
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• Grassed waterways
• terraces
• strip cropping along contour
• etc.

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Runoff from bare soil
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Use Multiple Tactics
Better nutrient timing, placement, and amounts
Reduce tillage
Reduce compaction
Cover crops
Healthier Crops
Better rotations
Control erosion
Add various sources of organic materials (crop
residues, manures, composts, etc.)
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