Transcript Document 7896465

Organic Matter
The key to healthy soils
Fred Magdoff
Dept. of Plant & Soil Science
University of Vermont
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
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
There are three general
“types” of organic matter in soils
 Living
 Dead
 Very Dead
bacteria
plant roots
nematodes
fungi
—Living —
earthworms
mites
moles
springtails
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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.
—Very Dead —
Well decomposed organic materials,
also called humus. Humus contains
very high amounts of negative
charge.
All three “types” of soil organic
matter play important roles in
helping produce high yields of
healthy crops.
Soil organic matter
Organic matter is 1-6%
of total soil mass
living
10-20%
humus active (dead)
(very dead) 10-20%
60-80%
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
Nutrient Availability
As organic matter is
decomposed nutrients
are transformed into
forms that are
available to plants.
From 50% to close to 100% of the CEC
is due to soil organic matter
Ca++ Ca++
- Ca++ - -- - + - K
Mg ++ -++
- Ca
a) cations
held on
humus
Figure 4.3
Ca++ Mg ++
- - -- K+
b) cations
held on
clay
particle
-
Zn ++
c) cations
held by
organic
chelate
Cation
Exchange
Capacity
Cation
nutrients
held on
negatively
charged organic matter and clay.
and Chelation
Corn grown in nutrient
solution with (right)
and without (left)
humic acids.
Photo by R. Bartlett.
Soil Tilth
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infiltration
runoff
a) aggregated soil
b) soil crusts after
aggregates break down
Root heavily infected with mycorrhizal fungi
(note round spores at the end of some hyphae).
Photo by Sara Wright.
Add
organic
matter
Increased biological activity
(& diversity)
Reduced
soil-borne diseases,
parasitic nematodes
Aggregation
increased
Decomposition
Pore structure Humus and other Nutrients
improved
released
growth
Harmful
promoting
substances
Improved tilth substances
detoxified
and water storage
HEALTHY PLANTS
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.
Water stable aggregates following addition of 1% dm basis of dairy
manure compost, small grain straw, grass clippings, or dairy manure.
62
60
Water stable
aggregates 0.25
to 4 mm diameter
as a percent of
total soil
58
56
Average for three
soils (sand, loam,
and clay)
a
b
54
52
b, c
50
48
46
44
42
40
c
c
ch comp. str. grass manure
Building Healthy Soils
2. Keep the soil covered with living
vegetation and/or crop residue.
 Use cover crops or perennial
sod cover routinely.
 Reduce tillage intensity.
Building Healthy Soils
3. Use better crop rotations.
 Grow perennials as well as
annual crops
 Different rooting depths
 Different growth and
harvest times
 Some high-residue crops
 Different crop families
 Etc.
Building Healthy Soils
4. Reduce tillage intensity.
 Many different reduced till
systems — conservation till,
ridge till, no-till.
 Better planters help.
 Cover crops can help.
Building Healthy Soils
5. Use other practices that reduce
runoff and erosion.
 Grassed waterways
 terraces
 strip cropping along contour
 etc.
Runoff from
bare soil
Runoff from
soil with
vegetative
cover
Use
Multiple Tactics
Reduce
tillage
Reduce
compaction
Better nutrient
timing, placement,
and amounts
Cover crops
Healthier Crops
Better
rotations
Add various sources of
organic materials (crop residues,
manures, composts, etc.)
Control
erosion