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Minnesota Watershed Nitrogen Reduction Planning Tool


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Using the nitrogen reduction planning model involves three steps. The first step is to select a watershed, enter hypothetical adoption rates for each BMP, and compare the effectiveness and cost of the individual BMPs. The second step is to compare suites of the BMPs that would attain any given reduction in the N load at minimum cost. The third step is to “drill down” to the details and assumptions behind the models of effectiveness and costs of any particular BMP and make any adjustments to reflect your particular situation.

Presentation by: William Lazarus

Published in: Education, Technology
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Minnesota Watershed Nitrogen Reduction Planning Tool

  1. 1. Minnesota WatershedNitrogen ReductionPlanning ToolWilliam LazarusDepartment of Applied EconomicsUniversity of MinnesotaDavid MullaDepartment of Soil, Water, and ClimateUniversity of MinnesotaDavid WallMinnesota Pollution Control AgencyDownload paper at:
  2. 2. Reasons for Study• Proposed MPCA standards for nitrate in surfacewaters• MN is part of a 12-state effort to develop a Gulf ofMexico nutrient reduction strategy.• EPA Science Advisory Board - 45% reduction in N andP is needed in the Mississippi River basin
  3. 3. PROJECT GOALS• Assess nonpoint source nitrogen contributions toMinnesota rivers from a) the primary land use sources,and b) the primary hydrologic pathways under dry,average and wet climatic conditions• Determine the watersheds which contribute the mostnitrogen to the Mississippi River, and combination of landuses and hydrologic factors having the greatest influenceson the elevated nitrogen• Develop a nitrogen planning tool to estimate reductions inN loadings to surface waters at the watershed scale withvarious BMPs, and their costs
  4. 4. Agroecoregion Based N Database• Point data are available for cropacreage and livestock numbers• County statistics are available forcrop harvest and N fertilizer use• N transformations in soil(mineralization, denitrification)and N losses (volatilization,leaching, drainage, etc) arebased on soil and landscapefactors (represented byagroecoregions)• Our approach is to estimate Ninputs and outputs foragroecoregion units and thentransform results back towatershed units
  5. 5. Leaching8.6Manure20.0Fertilizer70.3Deposition11.3Runoff0.8Drainage6.0CropRemoval111.6AnimalFeed38.6Milk, Eggs2.5AnimalsSold5.7Net Mineralization89.4Fixation + Seeds31.6 2.0Denitri-fication26.8Senescence37.3Manure and FertilizerVolatilization14.1Minnesota N Balance(lb ac-1)PurchasedAnimals1.6
  6. 6. N Loadings to Surface Water by Source
  7. 7. Effect of Climate on N Loadings
  8. 8. Watershed N Reduction Planning Tool• The Tool is an Excel spreadsheet linked to adatabase of Minnesota soils, landscapes,cropping systems, management practices andcrop enterprise budgets• Estimates of N reductions are based on researchmeta-data and BMP specific reductioncoefficients• Estimates are tied to site specific characteristicssuch as soil, slope, climate, and baseline farmmanagement practices and cropping systems
  9. 9. The 15 red- and brown-codedwatersheds are included in thespreadsheet planning tool.
  10. 10. N Reduction Planning Tool BMPs• Rate and timing of N fertilizer• Controlled drainage• Bioreactors• Planting cover crops• Planting perennial grass• Installing riparian buffer strips• Installing wetlands• Effects of individual BMPs as well ascombinations of BMPs can be evaluated
  11. 11. Note: The “Actual” rate is for all corn. The “max gross return” and “max net return”rates are for corn after soybeans.
  12. 12. N Fertilizer BMPs• Existing N rates can be reduced to target rates whichaverage 117 lb/ac for fall application in a corn-soyrotation.• Reductions in N loading are estimated based onempirical relationships for tile drainage, leaching andrunoff.• Spring or sidedress N rates are 30 lb/ac lower than fallapplications and reduce N losses by 8% compared to fall.• Spring application costs an extra$6-32/acre, while sidedressing costsan extra $24/acre.
  13. 13. Removing N from a Tile Line with a BioreactorThe diagram is an early design. Later designs are wider and shorter. The photoshows wood chips being placed in the plastic-lined trench near the outlet of the tileline.Source: Gary Sands, U of MN Dept. of Biosystems & Bioproducts Engineering
  14. 14. Suitable acres for BMPs• Fertilizer rate reductions are only possible in areas whereexisting application rates exceed Universityrecommendations• Controlled drainage and bioreactors can be installed ontile drained land with slopes of 0.5%, 1% or 2%• Perennial grass can be planted on ag land with cropproductivity ratings of 60% or less (marginal land)• Riparian buffers can be installed on ag land within 30 m ofwaterways• Wetlands can be restored on tile drained land with hydricsoils and high Compound Topographic Index values
  15. 15. User Inputs and Model Outputs• Select watershed and type of climate of interest• Select types of BMPs to install• Select percent of suitable acres in watershed forinstallation of BMPs• Model estimates effectiveness of each BMP atreducing N loadings• Model estimates cost (per lb of N removed or per ac)of installing each BMP• Model estimates overall watershed scaleeffectiveness and cost of installing multiple BMPs
  16. 16. Main Input Screen
  17. 17. “Effectiveness” is expressed as the N load reduction compared to thestatus quo. “Cost” is expressed per pound of N removed.-$10.00-$5.00$0.00$5.00$10.00$15.00$20.00$25.00$30.00$35.000.0%1.0%2.0%3.0%4.0%5.0%6.0%7.0%8.0%9.0%10.0%Cost/LbofNRemovedNReductionEffectiveness and Cost of Individual Practices, Le SueurRiver watershed, average weatherReduction in watershed N load N removal cost ($/lb N removed)
  18. 18. The “EfficientFrontier” of practiceCombinations.Reducing the N rateis expected toactually save moneyrather than increasecost.
  19. 19. Some are concernedthat corn yield lossescould result in a wetyear if some fertilizerN is lost. Here arethe results assuminga 33% loss offertilizer N.
  20. 20. Example Results for Three Watersheds(Average Weather Year)Water-shedCost/acreWater-shedcost ($mill)Cost/ lbof NActualreduc-tion Practices adoptedTarget N load reduction 12%Waton-wan R.-$2.52 -$1.15 -$1.14 12.6%reduce N rate 25%, spring preplant N2.8%, restore wetlands 4.0%, plant covercrops 8.9%Root R. $12.22 $9.80 $6.54 10.5%reduce N rate 19%, sidedress N 0.9%,riparian buffers 1.0%, restore wetlands0.6%, plant cover crops 5.9%, perennialcrops 1.2%SouthForkCrow R.$3.49 $2.09 $2.75 12.3%reduce N rate 23%, sidedress N 4.9%,restore wetlands 3.1%, controlleddrainage 0.5%
  21. 21. Conclusions• Total nonpoint source N loadings to Minnesotasurface waters were estimated at about 6% of thetotal inputs of N on all Minnesota cropland.• Statewide, losses of N to surface water fromagricultural sources represent 88% of total nonpointsource losses.• A tool was developed to assist planners evaluatestrategies for reducing N loadings to Minnesotasurface waters, by target watershed, climate, andextent of adoption of various N reduction BMPs.
  22. 22. Conclusions• The Tool estimates N loading reductions for individualpractices and for combinations of BMPs at the watershedscale• The Tool estimates costs associated with implementingBMPs– Cost/lb and cost/acre of individual practices– Net annual costs for implementing all BMPs in a selectedwatershed• Approaches to achieving N load reductions greater than25% are challenging.
  23. 23. Thank you• Support for this research was provided by theMN Pollution Control AgencyDownload paper at: