Organic Matter

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Organic Matter

• Chapter 6

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Black Gold
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After completing this chapter, you should be able
to

• Explain what organic matter is and how it forms
• Describe what organic matter does in the soil
• List several ways to maintain soil organic matter
• Discuss the problem of nitrogen tie-up
• Define organic soil, listing uses and problems

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• Organic matter consists of
• Animal and plant remains
• Roots, stems, etc.
• Leaves, grass clippings, compost, wood chips,
  mulch, etc.

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Chemical Makeupof O.M.

• Complex carbon compound chains
• Other elements attach such as
• N, O, H, S
• Carbohydrates are chains of simple sugars
• Sugars are short C chains with O
• Starches are a type of carbohydrate

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O.M.

• Many plant parts are made of cellulose, others
  carbohydrates
• Cellulose forms long fibers
• Most plant tissue is starch and cellulose
• Lignins are 10- 30 of plant tissue
• Lignins make the plant rigid

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Lignin
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O.M.

• Lignins are glued together cellulose fibers
• Lignins resist decay
• Lignins account for soil humus
• Proteins are chains of amino acids
• Short carbon chains of N and often S

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Decomposition of O.M.

• Carbon chains are broken down by soil flora into
  shorted chains, simpler compounds
• Decay resistant compounds are called humus
• Organic matter O2--gtCO2H2O humus

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Decomposition of O.M.

• Humus O2?CO2 H2O
• First reaction is fast, second one is slower
• Well drained soils lose 1-3 per year

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Humus

• Five factors effect the amount of O.M.
• Vegetation.
• Climate.
• Soil texture.
• Drainage.
• Tillage.

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Humus
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PrairiesGenerate the Most O.M.

• Humid tall grass prairie 5.8-7.6T/A/Yr
• N.Dakota mixed prairie1.4 T shoots
• 4T of roots

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ForestsHave the Least Soil O.M.

• The O.M. stays on the soil surface as leaf litter
  
• And in the canopy and tree stand
• There is 2x O.M. in prairie as forest
• O.M. extends deeper into the prairie
• Prairie O.M. returns to soil each year
• Forest O.M. does not

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Soil Profiles of Prairie and Forest Compared
O
A
A
AB
E
Bw
Bt

• C

C
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Conditions for O.M.

• Arid soils have less O.M.
• May gain O.M. with irrigation
• More Rain more O.M.
• Higher temp more O.M. but decays faster
• Cooler temp more O.M. (below 770F)

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O.M.

• Fine textured soils have more O.M.
• Wetter soils have more O.M. (less 02)
• O.M. improves conditions of mineral soils
• Increases water holding capacity
• Improves texture
• Stores nutrients in colloids and own chemicals

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Nutrient Availability

• Humus stores nutrients and makes some nutrients
  more available
• Releases mild organic acids which dissolve soil
  minerals
• Breaks down P compounds
• Chelates Fe and Z

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Soil Aggregation

• O.M. causes soil particles to clump
• Improves soil texture
• Improves resistance to break down
• Easier to work
• Better aerated
• Absorbs water

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Soil Aggregation
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Undesirable Effects of OgtMgt

• Nitrogen tie up
• Some plant residues are toxic
• Exampledead quack grass roots

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Maintaining Soil O.M.

• Maintain a higher input than loss
• O.M. naturally becomes C02?to the air
• O.M. produces a gum that glues soil particles
  together

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Conservation Tillage

• Moldboard tillage causes influx of O.M. and
  oxygen into the soil causing rapid decay. Bare
  soil is left to erosion
• Conservation tillage (no till) reduces oxygen,
  leaves material on surface for erosion control
• Holds more moisture, regulates temp

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Crop Residues

• Leaving crop residues provides O.M.
• Well fertilized crops leave more O.M.
• Green manure crops are plowed down instead of
  harvested
• You have to weigh the crop loss against the gains

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Crop Residues
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Crop Residues

• Leaving crop residues increase O.M.
• Exception is root crops
• Nationally about 1/3 of crop residue is used for
  food and bedding
• Fertilizing can increase crop residue

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Green Manuring andCover Cropping

• Traditional is main crop plowed down
• The loss of a paying crop for one season doesnt
  justify
• Legumes such as clover, alfalfa
• Grasses such as oats or rye
• Winter rye,fall planted spring plowed
• Companion crop between rows

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Crop Rotation

• Sometimes avoided because less valuable crops
  sometimes planted
• Improves soil O.M.
• Continuous crop reduces O.M.
• Grains cause smaller loss
• Meadow and hay increase O.M.

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Organic Matter Additions

• Manures
• Organic waste
• Sewage sludge
• Compost, leaves, grass clippings
• Crop only farms dont have manure
• Decayed sawdust or chips can be used

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Mulches

• Straw, clippings, leaves
• Reduces annual weeds
• Retains moisture
• Moderates soil temperature
• Not worth it on crops such as corn
• Increases yields on high value crops such as blue
  berries, raspberries, strawberries, tree fruits

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Maximum Cropping

• Cover soil as much as possible with crop
• Can double crop
• Can have two crops in a season
• Avoid fallowing

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Nitrogen Tie-up

• Soil flora need C and N to grow
• Flora will compete with plants for N
• Crop will show lack of N
• This is called carbon nitrogen ratio
• CN ratiowell rotted manure is 201
• Low CN ratio is nitrogen rich
• High CN ratio is N poor

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CN ratios

• Material CN ratio
• Soil humus 10
• Garden soil 12-15
• Compost 15-20
• Rotted manure 20
• Straw, leave 60
• Sawdust 400

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Nitrogen Tie-up

• Initial nitrogen level

Net gain Of nitrogen
Amount nitrogen
of organisms
Nitrogen Depression period
time
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Nitrogen Tie-up

• Occurs when low N materials are turned into the
  soil
• Rapid decay ties up usable N
• Surface material decay slowly
• Only N depletion at interface
• Plant crops after N depression or
• Add enough fertilizer to satisfy both

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Composting

• During composting the CN ratio narrows to about
  151
• At this point it can be added to the soil
• Dont use table scraps that attract animals such
  as rats.
• I was ordered by the city to remove my compost
  pile because of rats/mice) when I spread it there
  were no signs of critters

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Home compost pile
Organic material

• Enclosure
• Made of
• Fencing
• Or wire

Fertilizer Lime soil
Organic material (crop residue)
Organic material (grass clippings)
Organic material (manure)
Organic material ( leaves)
4ft to 10 ft in diameter
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Organic Soils

• Soils containing 20-30 O.M. are organic soils
• 1 out of 200 acres of American soil are organic
• Al,Mn,Mi,Fl,and Wi have the most acres of organic
  soil
• Organic soils form in bogs, marshes and swamps

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Organic Soils
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Organic Soils

• Wetlands often completely fill with organic
  deposits
• Some organic deposits can reach 80
• Peat Slightly decayed
• Muck fully decayed material
• Brown water from peat, muddy water from muck

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Organic Soils

• Fibricslightly decayed
• Hemic moderate decay
• Sapric most decayed
• Sphagnum peat is from sphagnum moss
• Hypnum peat is from hypnum moss
• Hypnum contains more lime/less acid

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Organic Soils

• Reed-sedge peat
• Forms in reed-sedge bogs
• Less acid
• More decomposed

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Organic soil profile

• Black spruce bog

Oi
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Organic Soils

• Lightest organic soil can weigh 1/20 as much as
  mineral soil
• Heaviest weighs about 1/3 that of mineral soils

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Organic Soils

• Sphagnum can absorb 20x its own weight
• Reed-sedge 5x its own weight
• Cultivated muck 2x
• Most organic soils are low in nutrients
• Muck soil N rich but low in P K
• Once fertilized retain nutrients

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Organic Soils

• Good for growing onions, celery, lettuce,
  carrots, mint, hay, turf
• Warms season crops dont do well
• About 700,000 acres yield 1billion/yr
• Once cleared, starts to disappear
• Called subsidence in Fl2-2 ½/yr

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Organic Soils

• Design drainage system to keep high water table
• Install sprinkler system
• Use wind erosion techniques but not tall
  windbreaks

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Organic SoilsUses for Peat

• Irish use for fuel(brewed alcohol often has smoky
  flavor)
• Used in soils mixes in nurseries and greenhouses
• Good for acid loving plants
• Hypnum is better for low acid plants
• Reed-sedge,for soil conditioning