Modeling Phosphorus Movement

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For more: http://www.extension.org/67713 Computer models are excellent ways to integrate years of scientific research into decision tools that producers and policy makers can use to reduce the environmental impact of agricultural phosphorus. Models are playing more important roles in efforts to manage phosphorus at the farm and watershed scales, so it is increasingly important to make sure models are well developed to meet the needs of users, give reliable predictions, and are consistently updated to keep pace with scientific knowledge.

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  • 1. Peter VadasUSDA-ARS, Dairy Forage Research Center, Madison, WICurrent Models for PhosphorusLoss from Agricultural Systems
  • 2. Agricultural P Loss? ItDependsHow do we effectively integrate decades of data andmultiple processes into comprehensive methodproducers, policy makers can use to make decisions?Soil P quantity and chemistryP Application rate and methodManure and fertilizer chemistryRunoff hydrologyErosionHow much does agriculture contribute to P pollution?What can producers do to decrease P loss? How do weanswer these questions?
  • 3. The Case for Models Due to sheer number of important physical andmanagement interactions, impossible to meet demandsfor information fast enough and cheap enough relying onfield research alone. Models are effective, efficient way to integrate variety offield data to make decisions. Some scenarios (climatechange, system integration) impossible to address withoutmodels. Model development forces us to formalize and testunderstanding of natural processes, and thus identifyknowledge and data gaps. Models are simple representations of our understandingof reality. Cant capture all complexities, what we dontknow.
  • 4. Current P ModelOptionsComplex SimpleSWATAPEXAnnAGNPSP IndexUser friendly,quantitativeAPLEWI SNAP+OK PPMTX TBET
  • 5. Complex P Models Daily time-step, field to watershed scale,quantitative predictions; For TMDL-type projects Process-based, spatially explicit simulations ofhydrology, multiple contaminant transport throughlandscape Data intensive for inputs and testing, extensiveuser experience and skill needed Should be calibrated Require dedicated support system for updating anddevelopment
  • 6. Simple P Indexes Annual time-step, field scale, relative ranking ofrisk of P loss Good for producer/policy education Not data intensive, little user experience andskill needed, no calibration needed Not process-based, calculations based on dataand professional judgment Generally had little field testing to verifyaccuracy of predictions and recommendations
  • 7. User-friendly,Quantitative P LossModels Models that estimate (lb/ac) annual, field-scale,P loss Moderate data requirements (mix of databasesand user-defined management) Require moderate user experience and skill, nocalibration needed Process-based equations based only onexperimental data, not spatially explicit Able to test with widely available P loss data
  • 8. Excel spreadsheet model that estimates (lb/ac)annual, field-scale, dissolved and sediment P loss insurface runoff for given set of management, soil P,erosion, runoff conditions.Intended to be process-based like SWAT, APEX, butuser-friendly like P Index.
  • 9. APLE Inputs
  • 10. Grazing AnimalsMilkCows HeifersDryCows CalvesTotal Cow Days (# cows x # days) 0 0 0 0BeefCows Calves0 0Solid Manure Applications Winter Spring Summer FallManure Applications Manure Applied wet ton/acre 0 0 0 0Manure Solids % 0 0 0 0Manure Total P2O5 Content lbs/wet ton 0 0 0 0Manure WEP/TP % 0 0 0 0Manure Incorporated % 0 0 0 0Depth of Incorporation inches 0 0 0 0Liquid Manure Applications Winter Spring Summer FallManure Applications Manure Applied gallons/acre 0 5000 0 5000Manure Solids % 0 6 0 6Manure Total P2O5 Content lbs/1000 gal. 0 6.1 0 6.1Manure WEP/TP % 0 50 0 50Manure Incorporated % 0 0 0 0Depth of Incorporation inches 0 0 0 0Fertilizer ApplicationsFertilizer Application Fertilizer P Applied lb/ac 0Fertilizer Incorporated % 0Depth of Incorporation inches 0Degree of Soil Mixing % 15APLE Inputs
  • 11. APLE OutputP Loss in Runoff0.00.51.01.52.02.51 2 3 4 5 6 7 8 9 10YearRunoffPloss(lb/ac)Soluble P from FertilizerSoluble P from ManureSoluble P from SoilSediment PMehlich 3 Soil P010203040506070801 2 3 4 5 6 7 8 9 10YearMehlich3SoilP(ppm)Top LayerBottom LayerWhole Topsoil
  • 12. APLE Testing P loss in runoff - Measured data from 28 cropstudies from 13 states, Australia, Ireland (Vadas etal., JEQ 2009), 14 grazing studies from 5 states,Australia, New Zealand (unpublished) Soil P dynamics - Measured data from 19studies monitoring changes in soil P from 1 to 25years (Vadas et al., JEQ 2012) Current updates include P loss from barnyardsand feedlots, uncertainty estimates
  • 13. Case 1: 50 STP, 1 ton/ac erosion, 3 in runoff, 45 lb P/ac liquid on surfaceCase 2: 50 STP, 3 ton/ac erosion, 6 in runoff, 45 lb P/ac liquid tilledCase 3: 50 STP, 5 ton/ac erosion, 9 in runoff, 45 lb P/ac liquid tilledCase 4: 100 STP, 1 ton/ac erosion, 3 in runoff, 45 lb P/ac liquid on surfaceCase 5: 100 STP, 3 ton/ac erosion, 6 in runoff, 45 lb P/ac liquid tilledCase 6: 100 STP, 5 ton/ac erosion, 9 in runoff, 45 lb P/ac liquid tilledKeeping P Loss Low
  • 14. 0.001.002.003.004.005.006.001 2 3 4 5 6 7 8 9 10RunoffPloss(lb/ac)Year0.001.002.003.004.005.006.001 2 3 4 5 6 7 8 9 10RunoffPloss(lb/ac)YearP Loss in RunoffSoluble P from FertilizerSoluble P from ManureSoluble P from SoilSediment P0204060801001201401 2 3 4 5 6 7 8 9 10Mehlich3SoilP(ppm)YearMehlich 3 Soil PTop LayerBottom LayerWhole Topsoil0204060801001201401 2 3 4 5 6 7 8 9 10Mehlich3SoilP(ppm)YearFeeding Less P0.5 % 0.3 %3 ton/acerosion6 in runoff45 lb P/acliquid onsurface9% less Ploss; 20%less soil P
  • 15. Soil P Buildup and Decline1.5 ton/acerosion5 in runoff45 lb P/acNo-tillManureapplied (180lb P/ac) andtilled onceevery 4 years
  • 16. Summary Models are effective way to integrate years of Presearch data to meet demand for managementand impact information fast and cheap. Models vary in complexity and appropriate uses,not always easy to know which one to choose andhow to use output. New P models help capture current science,balance versatility and complexity with user-friendliness Models are indispensible; need to be welldeveloped and tested, have committed supportfrom policy makers, scientists

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