Disturbance and recovery of soil C following infrequent activities

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Disturbance and recovery of soil C following
infrequent activities

• Rich Conant, Keith Paustian,
• Mark Easter, Amy Swan
• Natural Resource Ecology Laboratory
• Colorado State University

Supported by CASMGS-USDA/CSREES
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Background
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Background
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Background

• Periodic use of plow or chisel can increase
  yields
• In IL (58) and IN (77), most (corn/soybean)
  fields are in NT
• But, most (57 and 59) of those fields are under
  NT less than two years and the average time under
  continuous NT is less than 2.5 years.
• For MN, NT is less common (21 of all fields) and
  less than 10 have had continuous NT for more
  than one year

Source Hill, PM. 2001. Use of continuous no-till
and rotational tillage systems in the central and
northern corn belt. J of Soil Water Cons. 56
286-290

• How does soil C content for fields that are
  tilled occasionally from fields that are not
  tilled?
• How does inclusion of non-disruptive, high input
  crops impact soil C stocks?

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Literature data - tillage
Pierce et al. East Lansing, MI Continuous corn.
Decline in SOC stocks, but all treatments
mysteriously lost SOC. Declines greater for
tilled soils than for NT.
VandenBygaart et al. S. Ontario Cash-cropping.
Soil C distributed throughout the profile. No
measurable decline in SOC stocks.
Stockfish et al. S. Saxony NT SOC stocks
declined to match CT stocks after moldboard
plowing to 30cm.
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Literature data meadow/hay
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Observations

• From the published literature
• All results are solid published in the
  peer-reviewed literature
• Methods vary some (i.e., sampling depth, methods,
  etc.)
• We have every reason to believe the results
• But
• There are only a few published studies
• Results for those studies vary substantially from
  place to place
• This makes it difficult to draw conclusions about
  what might happen elsewhere
• Furthermore
• Infrequent activities and their impact on soil C
  stocks are not the focus for most agricultural
  field stations
• Incorporating variable tillage frequency or
  meadow duration into experimental design would be
  a challenge
• Integrating this type of experiment with other
  ongoing experiments is impractical

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Methods model, tillage impacts

• Century model
• Cultivation modeled as
• Transfer of organic matter from surface into
  soils (CULTRA)
• Multiplicative effect on organic matter
  decomposition (CULTEFF)
• Parameters vary from 1 to 6
• Values depend on degree of soil stirring and
  disruption

metabolic C
Lignin content
CO2
Structural C
Active C
CO2
CO2
CO2
CO2
Slow C
CO2
Passive C
CO2
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Methods model performance
Morrow Plots
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Methods model performance
Hoytville
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Methods sites, model runs
Sites E. Lansing, MI cool, mesic, 46 silt plus
clay, corn Hoytville, OH warm, mesic, 79 silt
plus clay, corn-soybean corn-oats-meadow Manhat
tan, KS warm, mesic, 92 silt plus clay,
wheat Sidney, NE warm, semiarid, 60 silt plus
clay, wheat-fallow (unique) Lethbridge, SK
cool, semiarid, 54 silt plus clay
fallow-wheat-wheat-hay
Model experiments NT, CT, NT2, NT4, NT6, NT8,
NT10 COM, COMM, COMMM, etc.
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Results tillage frequency
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Results tillage frequency
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Results tillage frequency
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Results tillage frequency
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Results meadow frequency
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Results hay frequency
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Results tillage frequency
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Results meadow duration
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Conclusions

• Tillage leads to decreased soil C stocks
• True at all sites, rotations
• Increased tillage frequency leads to greater
  declines in soil C stocks
• Responses vary from site to site
• Largest responses observed at E. Lansing, MI and
  Manhattan, KS
• Average NT2 was 90 of NT after 20 years and
  slightly greater for decreased tillage frequency
• Meadow/Hay in rotation can increase soil C
  stocks, but may not
• Inputs drive net soil C response (in model)
• This makes it difficult to draw conclusions about
  what might happen elsewhere
• Summary
• Infrequent activities can have a significant
  impact on soil C stocks
• Modeled responses are a result of disturbance and
  C inputs
• Improved yield assessments could improve results
• Tools exist with which to assess impacts of
  infrequent activities, but their accuracy needs
  to be evaluated