Kefyalew Girma Desta

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Building Soil Organic Matter in Organic
Production

• Kefyalew Girma Desta
• Oklahoma Cooperative Extension Service
• Plant and Soil Sciences Department

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Organic Matter MATTERS!
Organic materials are determinants of the health
of the soil
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Organic Material vs Matter

• Organic material is anything that was alive and
  is now in or on the soil.
• Organic material is unstable in the soil
• As much as 90 percent of it disappears quickly
  because of decomposition.

• When organic material decays to the point it is
  no longer recognizable
• 5 percent of it mineralizes yearly

• When the organic matter has broken down into a
  stable humic substances that resist further
  decomposition

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IT MEANS A LOT!

• Improve water infiltration rate/holding capacity
• Supply free nutrients
• Decrease pests, pollution from pesticides and
  heavy metals
• Soil pH buffer
• Improve soil tilth/ structure
• Reservoir of nutrients and water
• CEC
• C sequestration reduce CO2 and CH4
• Improve microbial mass and species diversity

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Water holding capacity
pH
If OMlt2.5, N,P and K leach away
Mielniczuk, 1996
NT vs CT
Infiltration
Prior et al., 2003
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. . . It means a lot!

• Effect on CEC

Effect on microbes, dairy manure
McLaren and Cameron (1996).

• Gardener et al.,2002 composting and compost
  proceeding

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Organic Material Decomposition

• Low CN ratios (lt201)
• mineralization and rapid rates of decomposition
• Undiluted manure and blood meal, grass clippings,
  vegetable wastes
• High CN ratios (gt301)
• immobilization and slower decomposition rates
• Straw, bark, wood chips, sawdust, paper,
  cornstalks, foliage
• Intermediate CN materials (201 301)
• Most composts, leaf mulches, cover crop residues

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First thing first!

• What is the goal?
• Short-term nutrient supply
• Slow nutrient supply
• Highly decomposable material vs slow decomposing
  materials
• Nature of the organic enterprise
• Soil type and problem

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Building Soil OM 3-Strategies

• Decrease losses
• Add Organic Material/Matter
• Consider Sustainability

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1. Building Soil OM decrease losses
Reduce tillage
Erosion control
Corn, Hussain et al., 1999, SSSAJ
Schertz et al., 1984, ASAE, proceeding
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. . . Decrease losses
Minimize monocropping
Corn, oats, wheat, clover, timothy, timothy,
100 yrs Gantzer et al. 1991, AJ 8374-77
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Building Soil Organic Matter Organic amendment
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Highly Variable

• Decomposition Contribution
• Nutrient content
• Availability
• Application
• Release pattern
• Winter early spring slow
• Late spring and summer rapid
• Fall release risk of leaching!
• Low nutrient content and availability

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1. Cover Crops

• Spring Annuals
• Oats and Triticale.
• Summer Annuals
• Buckwheat, Cowpea, and Sorghum
• Winter Annuals
• Austrian Winter Pea, Hairy Vetch and Winter Rye
  are planted in late summer/early fall, over
  winter, and resume growing the following spring.
• Biennials
• Yellow Blossom Sweet clover and perennials Red
  Clover can be grown for longer term
  soil-building.

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. . . Cover crops
Ability of cover crops to scavenge nitrogen (N)
in the fall and decrease leaching.
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. . . Cover Crops

• Common CN ratios of cover crops

If we return 2.2 tons/ac/yr of residue to the
soil, it will maintain soil OM at constant level
in continuously cropped soils.
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2. Green manure

• Non-legumes supply OM
• Legumes
• Both OM and fix N
• Legumes add 25-70 lbs N/ac

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. . . Green Manures

• Biomass and N yields of winter annual GM crops

Green manure crops can supply an OM equivalent
of 9 to 13 tons per acre of farmyard manure or
1.8 to 2.2 tons dry matter per acre. However,
the benefit from green manure crops soil
benefits will be gone in a year or less.
Schmid and Klay, 1984
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3. Animal Manure
Species, feed, and handling dependent
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4. Compost

• Low in nutrient
• Low availability
• More of OM buildup
• Very easy procedures available
• Any organic material can be composted
• Materials vary

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Compost vs Manure?
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5. Uncomposted Yard Debris

• Nutrient rich/poor, depends on material
• Better than compost
• Grass clippings release nutrients quickly 20 lbs
  N/wet ton, 5-20 is available
• Wood takes for ever!
• Leaves and small branches decompose quickly

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6. Packaged Organic Fertilizers

• Easy to use
• Less variable
• More concentrated
• Expensive!
• Blended forms

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Sustaining Soil Organic Matter
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Determination
Balance
Multi-dimensional
Courtesy of animation factory
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Indicators