1. Organic Matter The key to healthy soils Fred Magdoff
Dept. of Plant & Soil Science
University of Vermont

2. 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

3. 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

4. There are three general “types” of organic matter in soils
Living
Dead
Very Dead

5. plant roots
bacteria
nematodes
—Living —
fungi
earthworms
mites
springtails
moles

11. —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.

13. —Very Dead —
Well decomposed organic materials, also called humus. Humus contains very high amounts of negative charge.

14. All three “types” of soil organic matter play important roles in helping produce high yields of healthy crops.

15. Soil organic matter living 10-20% Organic matter is 1-6%
of total soil mass
humus
(very dead)
60-80%
active (dead)
10-20%

16. 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

17. Nutrient Availability

18. As organic matter is decomposed nutrients are transformed into forms that are available to plants.

19. From 50% to close to 100% of the CEC is due to soil organic matter

20. Cation Exchange Capacity
and Chelation

21. Corn grown in nutrient solution with (right) and without (left) humic acids.
Photo by R. Bartlett.

22. Soil Tilth

24. b) soil crusts after aggregates break down
infiltration
runoff
a) aggregated soil
b) soil crusts after aggregates break down

26. Root heavily infected with mycorrhizal fungi
(note round spores at the end of some hyphae).
Photo by Sara Wright.

27. HEALTHY PLANTS Add organic matter Increased biological activity
(& diversity)
Reduced
soil-borne diseases,
parasitic nematodes
Aggregation
increased
Decomposition
Pore structure
improved
Nutrients
released
Humus and other
growth promoting
substances
Harmful substances detoxified
Improved tilth
and water storage
HEALTHY PLANTS

28. 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.

29. Average for three soils (sand, loam, and clay)
Water stable aggregates following addition of 1% dm basis of dairy manure compost, small grain straw, grass clippings, or dairy manure. 62 a
Average for three soils (sand, loam, and clay) 60
Water stable aggregates 0.25 to 4 mm diameter as a percent of total soil 58 56 b 54 52
b, c 50 48 46 c 44 c 42 40 ch
comp.
str.
grass
manure

30. Building Healthy Soils
2. Keep the soil covered with living vegetation and/or crop residue.

31. Use cover crops or perennial sod cover routinely.
Reduce tillage intensity.

32. Building Healthy Soils
3. Use better crop rotations.

33. Grow perennials as well as annual crops
Different rooting depths
Different growth and harvest times
Some high-residue crops
Different crop families
Etc.

34. Building Healthy Soils
4. Reduce tillage intensity.

35. Many different reduced till systems — conservation till, ridge till, no-till.
Better planters help.
Cover crops can help.

37. Building Healthy Soils
5. Use other practices that reduce runoff and erosion.

38. Grassed waterways
terraces
strip cropping along contour
etc.

39. Runoff from soil with vegetative cover
Runoff from bare soil
Runoff from soil with vegetative cover

40. organic materials (crop residues,
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.)