Organic Amendments

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Organic Amendments
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Organic Amendments BenefitsSoil Fertility

• N release depends on nature of material, CN ratio

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Sunn Hemp Hay for use as Amendment
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Cowpea Cover Crop and Hay
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Pepper Yield following MSW Compost
With Compost
No Compost
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Practicality of Amendments as N Fertilizer Sources
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Organic Amendments BenefitsSoil Fertility

• N release depends on nature of material, CN
  ratio
• Must match N supply and demand curves

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Crop Demand for N
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Supply of N after decomposition of organic
amendment
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Supply of N after decomposition of organic
amendment
If amendment applied too early, N may be released
before crop needs it
Synchronize N release and crop demand
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Organic Amendments BenefitsSoil Fertility

• N release depends on nature of material, CN
  ratio
• Temperature affects decomposition and nutrient
  release, which can be very quick in warm climates
• If decomposition of amendment (in soil) is too
  fast, may need to keep it on surface as a mulch

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Mulches on plots, can become amendments as they
decompose
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Whole Plant Materials as Mulch
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Organic Amendments Benefits

• Soil fertility
• Benefits of green manures in some cases (green
  manure legume residues are common amendments)
• Increased soil organic matter
• Pest management

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Organic Amendments BenefitsIncreased Soil
Organic Matter

• Improved water holding capacity
• Improved nutrient cycling
• Slows pesticide leaching reduced groundwater
  contamination

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Organic Amendments BenefitsPest Management

• Provides environment for biological control
  organisms
• Toxic products from decomposition may affect
  pests, best documented examples
• Neem (leaves and other parts of Azidirachta
  indica) a natural insecticide, effects on
  nematodes as soil amendment
• Crucifer residues (cabbage, etc.) effects on
  some soilborne plant pathogens biofumigants,
  release isothiocyanate

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Organic Amendments BenefitsPest Management
Many claims, not all well documented !

• Yield responses often seen without pests present
• Maybe pest reduction occurs too but need data as
  proof to show this

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Organic Amendments BenefitsPest Management
Many claims, not all well documented !

• Yield responses often seen without pests
• Maybe pest reduction occurs too but need data as
  proof
• Mechanisms

OM Decrease Increase
Pest Yield
OM Decrease Pest
Increase Yield
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Compost

• product of natural decomposition when organic
  matter is broken down
• an intermediate stage in the decomposition
  process

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Composts

• N availability and breakdown of composts and
  organic amendments

Organic N,C,H,O Decomp. CO2,
heat, NH3
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Speed of decomposition and N availability depends
on CN ratio

• Immature or unstable compost (CNgt301)
• Mature or stable compost (CNlt201)
• Very low CN or materials rich in NH3 can result
  in too rapid release of NH3 phytotoxicity

N rob soil N temporarily immobilized by
microorganisms using excess C from compost
temporary N deficiency in soil limited early
growth of crops
N mineralized as NH4 or NO3- uptake by
plant for good growth
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Heat and Compost

• High temperatures (60-80C, 140-175F) generated
  in compost piles by thermophilic bacteria
• No heat benefit as compost is amended into soil
  (cant kill soil organisms by this heat)
• Heat can kill disease organisms in the compost
  pile
• Risky to use diseased material in compost (might
  survive at edge of pile, etc.)

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Source of Mulches, Amendments, Composts can
affect quality

• Heavy metals, plastics, etc., can accumulate from
  use of some materials if source has been
  contaminated by these undesirable products
• Possibility of introducing plant disease, N rob,
  or NH3 toxicity

Caution watch out for urban waste products,
heavy metals
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References

• Text, Ch. 14, pp. 295-305.
• Altieri, 1987. Ch. 10.
• Brady, 1974. Ch. 8.