Rapple "Scholarly Communications and the Sustainable Development Goals"
Southern SAWG - Basic Organic Soil Mnagement
1. Basic Organic Soil Management:
Caring for the Soil as a Living System
Southern Sustainable Agriculture Working
Group Annual Conference
Mobile, AL – January 18, 2014
2. “Feed the soil, and the soil will feed the crop”
David O’Neill of Radical Roots Farm in central Virginia
maintain a healthy, living soil, the foundation of
successful farming.
3. Part One
Feeding and Protecting the Soil
• Conservation – prevent erosion losses
• Soil life – the “livestock” on every farm
• Habitat – organic matter and tilth
4. First, keep the soil on the farm!
Once the topsoil is gone, it’s gone
(left). Nature builds an inch of
topsoil every 300 – 500 years. Yet,
good soil conservation and organic
soil management can restore
fertility in three to ten years (above).
5. Four Principles of Soil Health
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Keep soil covered as much of year as possible.
Maximize living roots in the soil profile.
Minimize soil disturbance.
Energize the soil system with biodiversity.
– Multi-species cover crops - 5 or more species from
3 or more plant families
Based on the work of the NRCS Soil Health Team in Greensboro,
NC – David Lamm, Ray Archuleta, Steve Woodruff, and Terry
Briscoe
6. Key Elements of the Soil Food Web
Multiple trophic levels convert residues to soil organic matter
7. Plant Roots
Play a Vital
Role in the
Soil Food Web
• Root exudates
and fine roots
• Rhizosphere
community
• Mycorrhizal
fungi
8. The Organic
Matter Cycle
The soil food web is
the engine of soil
fertility and plant
nutrition. The
breakdown of
organic residues is
the sole source of
plant nutrients,
except for nitrogen
fixed by microbes.
N-P-S
9. The Organic Matter Cycle in Nature
The organic matter cycle provides all the nutrients for
plant growth in natural ecosystems such as this forest.
10. The Organic
Matter Cycle in
Agriculture
• Harvest removes
organic matter (OM)
and nutrients.
• Bare soil periods
reduce OM input.
• Tillage burns up OM
and promotes
nutrient leaching.
11. Replenishing the Organic Matter Cycle
To make up for these losses and maintain soil
health, feed the soil life a “balanced diet” of:
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Cover crops and green manures
Compost
Organic mulches
Crop residues
Manure
Organic fertilizers and amendments
12. Cover Crops: the Cornerstone of
Sustainable Crop Production
Cover crops maintain soil
quality by:
• Preventing erosion,
compaction, crusting
• Adding organic matter
• Feeding the soil life
while alive (root
exudates)
after termination
Triticale + Field Pea
13. Cover Crops: the Cornerstone of
Sustainable Organic Crop Production
Cover crops provide and
manage nutrients by:
• Fixing N (legumes)
• Scavenging surplus N
• Making scarce P (legumes,
buckwheat) and K
(grasses) more available
• Not aggravating P or K
excesses when these exist
Crimson Clover
14. Cover Crops: the Cornerstone of
Sustainable Organic Crop Production
Cover crops reduce
pest problems by:
• Suppressing weeds
• Breaking pest and
disease life cycles
• Providing habitat for
beneficial organisms
Buckwheat
15. Living Plant Cover is Vital
to Soil Health
Bare soil is hungry,
stressed, and at risk
(not “resting”) …
and is an invitation to
weeds.
Minimize bare
fallow periods in crop
rotations.
16. Living Plant Cover is Vital
to Soil Health
This vigorous cover
crop supports a
thriving soil food web
through abundant root
exudates and
sloughing of fine roots.
This is the right way to
“rest” the soil.
Winter Rye + Hairy
Vetch
17. Managing High Biomass Cover Crops
Pearl millet + sunnhemp: 7 feet, 4 tons/ac in 65 days.
Mow, scythe, or weed-whack top growth.
Using clippings as mulch or to make compost.
Till stubble as needed to prepare ground for next crop.
18. Compost: a Concentrated Soil Food Web
Composting facilitates the
conversion of raw organic
residues of plant and
animal origin into active
organic matter and humus
by mixing materials in a pile
or windrow,, and managing
temperature, aeration, and
moisture.
19. Composting Tips
• Start with diverse mix of organic materials.
• Balance carbon & nitrogen – C:N ratio 25-35:1
Use 2 – 3 parts plant matter and 1 part manure.
• Maintain optimum moisture – 50 – 60%.
• Turn windrow to aerate and compost all parts.
• Heating to 135 – 150°F for 15 days kills pests,
pathogens, weed seeds. Avoid temps > 150°F
• Cool curing period (2-6 months) builds beneficial
microbiota.
20. Good, finished compost provides:
• Inoculum of beneficial
soil organisms
• Active organic matter
• Stable humus
• Nutrient and moisture
holding capacity
• Slow-release nutrients
Finished compost produced
• Extra P, also K, S,
at Poplar Manor Enterprises
micronutrients
in Riner, VA
21. Manure: the Original Organic Fertilizer
Manure benefits:
Manure cautions:
• Provides N, P, K, and
micronutrients.
• Supports beneficial
soil life.
• Promotes heating and
provides nutrients in
compost pile (20-30%
of total mix).
• Unstable N
• Pathogens
• Antibiotic and
herbicide residues
• Weed seeds
• Salts
• Unbalanced N:P ratio
• Cu and Zn buildup
(poultry litter)
22. Manure Management
• Know the source, avoid chemical residues.
• Compost or age with carbon (e.g. bedding) to
stabilize nutrients and reduce pathogens.
• Compost at ≥131°F for 15 days, or apply at least 120
days before harvest to protect food safety.
• Spread on heavy feeding cover crop.
• Adjust rates to optimize soil P and other nutrients.
• Avoid nutrient runoff – do not spread on bare or
frozen soil on sloping fields near streams or ponds.
23. Organic Mulch: Simulating Nature’s
Way of Feeding the Soil
Organic mulches:
• Protect the soil surface.
• Conserve soil moisture.
• Suppress annual weeds.
• Feed the soil life.
• Provide slow-release
nutrients.
• Provide habitat for
spiders and other
generalist pest predators.
Eggplant thriving and nearly
weed-free in straw mulch at
Dayspring Farm in the
Tidewater of Virginia
24. Mulching cautions:
• Weed seeds
• Herbicide residues in hay (especially
picloram, clopyralid, aminopyralid,
aminocyclopyrachlor)
• Cooler soil
• Potential pest habitat (slugs, squash bugs)
• Excess K with heavy use (esp. grass hay)
• Costs of purchase, hauling, and spreading
25. Plastic Mulch
• Better weed control
• Warms soil
• Practical at farm scale
However:
• Does not feed soil life,
may stress earthworms
and other organisms
• Planting holes and alleys
need other weed control.
• Must be removed at end
of season
Black plastic film warms soil
and suppresses weeds near
crops. Alley weeds must
be controlled by other means.
26. Building and Protecting Soil
While Using Plastic
Covering alleys with organic
mulch (above) or a rye + clover
cover crop (right) protects soil in
alleys and adds organic matter.
27. Soil Health Challenges for Vegetable
Production in the South
• Many vegetable crops return little residue to
feed the soil life.
• Farmers working small acreages must crop
intensively to make a living, have less
flexibility to include soil building cover crops.
• Warm, rainy climates accelerate organic
matter oxidation in Southern region soils,
especially in tilled annual cropping systems.
28. The Organic Grower’s Dilemma
• Organic producers aim to
build soil life and organic
matter for long term fertility.
• Without herbicides, organic
systems depend on tillage
and cultivation to manage
weeds and cover crops.
• Tillage burns up organic
matter, and each pass
stimulates more weed seeds
to germinate.
Plowing down vetch cover
releases N, but leaves the
soil exposed, and may cause
a flush of weed emergence.
29. Tips for Maintaining Soil Quality
while Growing Organic Vegetables
• Keep soil covered with
living plants – as soon as
one crop is harvested,
plant the next!
• Include one high-biomass,
multi-species cover crop
per year in the rotation.
• Reduce tillage whenever
practical.
30. Crop rotation and intercropping in a short
growing season
In central Vermont, Eliot Coleman
maximized year-round ground
coverage by interplanting cover
crops into vegetables at midgrowth.
31. Reducing tillage to save organic matter
Reduce tillage when
practical:
• No-till into rolleddown cover crops
• Mulch tillage (≥30%
residue coverage)
• Ridge tillage (skim top
of ridge to plant crop)
• Strip-till (disturb soil
only in crop row)
Demonstration of no-till vegetable
transplanter in roll-crimped cereal
grain cover crop at North Carolina
Agriculture & Technology State U.
32. Perennial sod to restore soil and
reduce weed populations
Include perennial sod crops
in the rotation to restore soil
quality and reduce weed
seed populations.
• Cereal grain + red clover
for 1 year
• Perennial grass + legume
for 2 – 4 years
After several years’ vegetables,
oats + red clover were planted.
Clover was grown for one year
after oats were harvested.
33. On slopes greater than 5 – 7%, grow
perennial crops
At Virginia Gold Orchards, 28 acres of Asian pears on hilly
ground in Lexington, VA, Paul and YoungSuk Estabrook
combines a high-value crop(left) with soil conserving
perennial sod between rows of trees (right).
34. Part Two
Feeding the Crop
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Meeting crop nutritional needs
Optimizing efficiency, avoiding pollution
Understanding soil tests
Developing organic recommendations
35. Can “Feed the Soil”
adequately feed the crop?
• Healthy, well-fed soil food web can meet most
of the crop’s nutrient needs.
• Usually need some nutrient inputs.
• NPK input needs are often less than
conventional recommendations.
• Replenish organic matter to maintain soil life.
36. How the Soil Life Modulates Crop Nutrition
Nitrogen is initially tied up as microbes digest fresh residues, then
gradually released as higher trophic levels consume microbes.
37. Organic Nutrient Management
Use organic and natural mineral amendments to:
• Restore depleted soils
• Remedy nutrient deficiencies & imbalances
• Adjust soil pH
• Meet nutrient demand of heavy feeders
• Replenish nutrients removed in harvest
38. Determining Fertilizer Needs: Soil Test
A soil test is a “snapshot” of the chemical
condition of the soil, including:
• pH (acidity)
• Plant-available P, K, Ca, Mg, micronutrients
• Organic matter content
• Cation exchange capacity (CEC)
• Recommendations for lime, nitrogen (N),
phosphate (P2O5), potash (K2O)
39. Interpreting the Soil Test
• VL = very low
critically deficient
• L = low
likely yield limiting
• M = medium
possibly yield limiting
• H = high
optimum for most crops
• VH = very high
possibly excessive
40. Understanding conventional nutrient
recommendations
• Lime recommendations based on soil pH, CEC, and
buffer index.
• NPK recommendations based on research into crop
responses to nutrients on conventionally managed
soils.
Usually more than harvest removal, because some of
applied soluble NPK is lost or tied up.
Biologically active soils often need less inputs.
• Can use organic fertilizers to provide recommended
nutrients.
44. Nutrient
Deficiency
Scenario 2: The
soil life is depleted
or unbalanced.
Utilize high
quality compost
to provide
inoculum.
Provide organic
inputs to “feed”
soil life.
46. Tips on Using a Soil Test in
Organic Nutrient Management
• Correct sampling procedure is important.
• Note deficiencies, excesses, and imbalances.
• Observe the soil and crops.
• Verify with plant tissue analysis.
• Re-test with same lab to monitor trends.
47. Soil pH and Lime
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Most vegetables prefer pH 6.0-7.0.
Blueberries prefer pH 4.8-5.2.
Use high-calcium limestone if Mg is high.
Use dolomitic limestone if Mg is low.
Use elemental sulfur to lower pH.
Hydrated lime and quicklime are hard on soil
life; not allowed under NOP certification.
48. Nitrogen (N)
• N is most common crop
nutrient deficiency.
• Vast stores in atmosphere (N2),
and soil (organic matter N)
• Plants utilize soluble nitrate
(NO3-) or ammonium (NH4+).
• Soil life mediates N availability
and storage.
• Legumes important N source.
• Soluble N easily leached or
volatilized, can pollute water.
Deficiency: older leaves
turn evenly yellow.
49. Carbon-to-Nitrogen (C:N) Ratio
and Soil N Dynamics
• Soil life utilizes 25-30 lb C for every lb N.
• Organic residues with C:N > 30:1 tie up N.
• Organic residues with C:N < 25:1 release N.
• Materials with C:N 25-35:1 build most soil OM.
• Biological processes reduce C:N of materials.
50. Organic and natural mineral N sources
Legume cover crops (can add 50-200 lb/ac)
Feather meal (13-0-0)
Blood meal (12-0-0)
Chilean nitrate (16-0-0)
N sources with some P and K:
Cottonseed meal (6-2-1)
Fish Meal (9-3-1)
Harmony (poultry litter) (5-4-3)
Composted manure (~ 1-1-1 to 2-2-2)
51. Nitrogen Budgeting in
Organic Farming
Estimate N available to the current crop:
• Estimate N from mineralization by soil life (50 –
200 lb/ac-year – released most efficiently during
warm season)
• Legume cover crops (~50% of total N)
• Manure (~50% of total N)
• Compost (10-25 % of total N)
Apply organic N fertilizers as needed
52. Phosphorus (P)
• Plants use soluble phosphates.
• Most soil P = insoluble mineral
and organic forms.
• Soil life mediates P availability;
mycorrhizae play vital role.
• P excesses initially “fixed,”
then accumulate in soil.
• P is lost in runoff and erosion,
can pollute surface waters.
• P is most limiting worldwide.
Deficiency: stunted
growth, purple or
reddish leaves
53. Organic and natural mineral sources of P
Rock or colloidal phosphates (0-3-0)
total (0-20-0) available over ~10 yrs
Bone meal (2-14-0) – faster release
Manure, fresh or composted, 1-2% P2O5
Composted plant matter, 0.2-0.8% P2O5
Poultry litter based fertilizers (Harmony, 5-4-3)
1 lb P2O5 = 0.44 lb P
54. Nitrogen-Phosphorus Balance
• Plants utilize N and P in a ratio of 6:1 – 10:1.
• Manure and compost provide N and P at
about 3:1.
• Some manure N is lost, P is stable.
• Using manure or compost for N can build up P.
• Excessive soil P can inhibit mycorrhizae, upset
plant nutrition.
• Legume cover crops add N but not P.
55. Managing N and P in organic systems
If soil P is low:
• Compost can be used
generously, 10-20 t/ac
annually, to provide N
and build organic matter
If soil P is high:
• Limit compost to match P
inputs with P removal –
about 2-4 tons/ac-year
• Use legumes, blood meal,
feather meal, etc. for N
Broccoli requires 150 lb N/ac
within 60-70 days after
planting. Supplying it all with
manure or compost will build
up soil P.
56. Potassium (K)
• Plant-available K as K+ ions,
held on CEC (clay + humus).
• Most soils have large
insoluble mineral K reserves.
• Cereal grains, grasses, trees
release some mineral-fixed K.
• Vegetables use a lot of K (≥ N).
• K surpluses can build up in
most soils.
Deficiency: white spots,
• K can leach from sandy soils;
singed or tattered
not considered polluting.
edges on older leaves
57. Organic and natural mineral sources of K
Potassium sulfate (0-0-51-18S, rapid release)
Sul-po-mag (0-0-18-11Mg-22S, rapid release)
Greensand (7% K, very slow release)
Grass hay mulch (~2% available K)
(spoiled hay sometimes available free)
Liquid K foliar fertilizers available (6% K)
1 lb K2O = 0.83 lb K
58. Potassium and Nutrient Balance
• Hay or grass mulches are very rich in K.
• Excess K can interfere with Mg or Ca nutrition:
Blossom end rot, tip burn in vegetables.
Grass tetany in livestock (life-threatening).
• K excesses are fairly easy to draw down.
59. Magnesium (Mg)
• Plant-available Mg is
mostly held on CEC as
Mg++ ions.
• Deficiencies occasionally
occur.
• Magnesium sources:
Dolomitic lime
Sul-po-mag (also adds K)
Magnesium sulfate
Deficiency: older leaves
yellow between veins.
60. Calcium (Ca)
• Plant-available Ca held on CEC as Ca++ ions.
• Ca is usually sufficient if soil pH ≥ 6.0.
• Blossom end rot (tomato, pepper) and tip burn
(greens) are localized Ca deficiencies.
• Sources of Calcium:
– High calcium limestone, aragonite (raises pH)
– Dolomitic limestone (raises pH, also adds Mg)
– Gypsum (does not affect pH, also adds sulfur)
– Poultry litter based fertilizers (~9% Ca, raises pH)
61. Sulfur (S)
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Most topsoil S in organic forms.
Plants utilize soluble sulfate-S.
Sulfate-S can leach from topsoil.
Many Virginia soils have good
subsoil sulfate-S reserves.
• S deficiency most common in
seedling stage, sandy soils.
Deficiency: youngest
• Gypsum, sul-po-mag,
leaves turn evenly
magnesium sulfate, and
yellow.
elemental sulfur supply S.
63. Amending micronutrients
• Boron (B) deficiency is
common in Virginia.
• Zn, Cu, Mn are occasionally
deficient.
• Poultry litter is Zn and Cu
source.
• Molybdenum occasionally
deficient in legumes.
• NOP allowed micronutrient
supplements are available.
Acute B deficiency:
distorted or damaged
growing points.
