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
              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)
• now phosphorus recognized as having role in
• no one answer to fix problem
  – both agriculture and people (sewage effluent)
• recommended 45% reduction in N and P
  going down Mississippi River
River Basin
Mississippi River Basin Phosphorus
Major Mississippi Subbasins
Major Mississippi Subbasins
  loads for
2001 to 2010
 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

                +             +

- 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
    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
  – can be > 100% in heavily tile drained watersheds
Drainage by tiles and ditches
Patterned tile
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
• 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
     P from
    fields to
     rivers –

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

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
    – Lake
    – Saylorville
• 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
• 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
• 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
• 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
• just targeting a few fields will solve most of
  the problem
• edge of field denitrification can solve the
• 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
• many (most?) practices to reduce nutrient
  loss don’t increase yield

• N and P balances don’t relate well to nitrate and P loss
  across the MRB (but could increase losses in a drought
• 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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