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Overview of Nitrogen Mass Balances in Agricultural Ecosystems

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Overview of Nitrogen Mass Balances in Agricultural Ecosystems Powered By Docstoc
					  Overview – Nutrient
  Fate and Transport

              Mark B. David

University of Illinois at Urbana-Champaign
Presented at Building Science Assessments
   for State-Level Nutrient Reduction
               Strategies
              Nov. 13, 2012
                 What I will cover
• what the problem is
• N and P sources, balances, and river exports in the
  Mississippi River Basin (MRB)
   – Illinois as example
   – what is going to the Gulf

• importance of modified hydrology (tile drainage)

• timing of flow and nutrients; fate

• myths; the challenge ahead
          What is the problem?
• both local and
  downstream water quality
  problems from nitrate
  and total P
  – local: algal production due
    to P; drinking water for N
  – downstream: hypoxia in
    the Gulf of Mexico

• USEPA requiring nutrient
  criteria in flowing waters
Hypoxic zone, 2012
 What was new (in 2007, now old)

• reaffirmed previous assessment
• importance of spring (April, May, June)
  nitrate
• now phosphorus recognized as having role in
  Gulf
• no one answer to fix problem
  – both agriculture and people (sewage effluent)
• recommended 45% reduction in N and P
  going down Mississippi River
Mississippi
River Basin
 Nitrogen
Mississippi River Basin Phosphorus
Major Mississippi Subbasins
Major Mississippi Subbasins
  Nutrient
  loads for
2001 to 2010
  Nutrient
 yields for
2001 to 2010
Spring nitrate, upper Miss and Ohio
Source of spring nitrate
             County Level Analysis of
              Mississippi River Basin

    • counties in MRB (all 1768)
    • 1997 to 2006 annual data on fertilizer,
      crops, animals, people, deposition
    • predictive model from watersheds applied
      to all MRB counties
    • both N and P



From David et al. (2010)
            Nutrient Balances
inputs



                +             +




- outputs



            -             -
         Annual N Fertilizer Applications




Fertilizer (kg N ha-1)
     0.0 - 11.2
     11.3 - 27.2
     27.3 - 45.4
     45.5 - 65.9
     66.0 - 107.1                 From David et al. (2010)
       Tile drainage is concentrated in the
                     corn belt




Fraction of county




                                  From David et al. (2010)
            Net N Inputs (NNI)




kg N ha-1




                   Some counties negative, N from soil mineralization
Illinois N
 budget
 through
   2012
    Linking N balances to N Export

• hydrology overwhelming factor
  – channelization, tile drainage
• can look at watershed N export as a fraction
  of net N inputs
  – most studies, about 25%
  – however in MRB we know it is larger in critical
    areas
  – can be > 100% in heavily tile drained watersheds
Drainage by tiles and ditches
Patterned tile
   systems
Embarras River - Camargo
Embarras River
Embarras River
Modeled January to June Nitrate Export




        Best model includes fertilizer, sewage effluent,
        and tile drainage
    Components of P Mass Balances
• net P inputs
  = inputs – outputs
    inputs (fertilizer)
    outputs (grain harvest - human and animal
    consumption)
• net indicates additions or removals from soil
• little P (relative to N) is lost to streams, but
  it is biologically important
• surface runoff and tile leaching
• manure
Fertilizer P       Row Crop %




Manure P       Net P Inputs




                   From Jacobson et al. (2011)
Modeled January to June Total P




                       From Jacobson et al. (2011)
Illinois P
 budget
through
  2012
     P from
    fields to
     rivers –
    Embarras
      River


From Gentry et al. (2007)
   Particulate
     P from
    fields to
     rivers




From Gentry et al. (2007)
Importance of a Few Storm Events




                       From Royer et al. (2006)
                      Fate of N
• limited in-stream
  losses of nitrate
  during high flow
  periods
    – Lake
      Shelbyville
    – Saylorville
      Reservoir
• retention times
  too short
• spring nitrate,
  headed to Gulf
                    Fate of P

• some sediment removal
• problem of sediment
  already in streams/rivers
  – stream bank, bed erosion
• algal biomass can move
  downstream
• no way to easily get out
  of system (like nitrate)     Source: Clay Soil and Water Conservation
                               District, Minnesota
 What we know about nutrient sources

• Upper Mississippi and Ohio
  subbasins are the major
  source of nitrate and total P
  – even more so in critical spring
    period
• the tile drained cornbelt is
  clearly identified
• mass balance of P has greatly
  decreased, but not N
    What can we do in agriculture?
• given,
  – it is not typically over fertilization
    based on current rates and yields
  – may be zero or negative N & P balances
    in some areas of the tile drained
    Midwest
• three types of conservation
  practices could help
  – nutrient-use efficiency
  – in-field management
  – off-site measures
Potential Efficiencies -SAB report
Perennial biofuels quickly reduce
           nitrate loss




                           From Smith et al. (2013)
           Point sources in MRB?

• sewage effluent and
  industrial (22% of annual
  N and 34% of P)

• however, only 14% (N) and
  20% (P) of spring load

• not going to solve problem,
  but could help for P
                A few myths

• no-till solves all problems
• a few (bad) actors are the problem
• over application of N (or P) is most of the
  problem
• just targeting a few fields will solve most of
  the problem
• edge of field denitrification can solve the
  problem
• the response will take a long time (decades?)
    What’s making it difficult

• more corn (and fertilizer)
• more intensive tile drainage
• warmer winters
• more intense winter/spring precipitation
• fall N in Illinois, Indiana, Ohio
• the intensity of agriculture across the
  cornbelt
• many (most?) practices to reduce nutrient
  loss don’t increase yield
                   Conclusions

• N and P balances don’t relate well to nitrate and P loss
  across the MRB (but could increase losses in a drought
  year)
• counties with high fertilizer inputs have high crop
  fractions (& corn acres) and tile drainage
   – all lead to nitrate loss
   – corn & soybeans on tile drained land much more important
     than manure, deposition, or sewage effluent
• P from both surface runoff and tiles
   – sewage effluent also important
• high winter/spring flow and nutrient losses are a
  challenge, and seem to be getting worse
               Job ahead for us

• 45% reductions in N and P will be quite difficult
  in upper MRB
• we haven’t really started
  – not in any meaningful way
• variety of methods and costs
  – many or most unrelated to yields
• scale of problem is impressive
• but, we do know how to do it!

				
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posted:6/20/2013
language:English
pages:47