Annual P Loss Estimator (APLE) User-friendly Model for Annual, Field-Scale Phosphorus Loss Peter Vadas USDA-ARS Madison, WI
Phosphorus input to water bodies continues to be an issue Agriculture continues to be identified as important source of non-point phosphorus
What do we need to know about P loss from farms? How much is lost? How much is transferred? What s the impact?
How do we estimate how much P is lost? We measure. Scenarios to monitor? Soil (clay, OM) 4 Soil P status x 3 Erosion rate (land use, tillage) x 4 Runoff amounts x 3 P application rate x 3 P application type (fertilizer, animal species) x 3 P application method (surface, injected) x 3 Years of weather x 3 11,664 We can t possibly measure everything everywhere. How should we identify fields or practices that need attention? Computer models are an important tool.
Models can be cost and time-effective
weather landscape fertilizer manure soil P soil We know P loss is complex, but our decisions are limited by ability to process only a few interactions at a time. Models allow us to Drainage Runoff Erosion Soluble P 1. Map out all interactions to see how they influence P loss 2. Find practices with greatest impact, negative and positive 3. Identify the most important knowledge gaps (research) 4. Make decisions based on information beyond our own experiences management Sediment P
Models make us nervous They are black boxes
Models make us nervous, cont
When should we use a model? We feel models improve our ability to make decisions because we Understand and agree with science and data behind them Understand and agree with how they work and generate output (transparency) Agree with how they are used given their structure and processes Need monitoring and modeling whole greater than sum of parts
Current P loss model options Complex, quantitative SWAT APEX Bay Model User friendly, quantitative APLE Simple risk assessment P Index Farm to Watershed Field Field
APLE Properties Excel spreadsheet model that estimates (lb/ac) annual, field-scale, dissolved and sediment P loss in surface runoff Intended to function like a P Index Estimate P loss for given set of management, soil P, erosion, runoff conditions Be more process-based than most P Indexes, but much more user-friendly than APEX, SWAT type models
APLE Inputs
APLE Inputs
Dissolved P Loss from Surface Manure, Fertilizer P applied - P into soil from tillage, liquid manure infiltration (Vadas, 2006) P on surface X Availability factor Fertilizer: 100% Manure: % WEP (Vadas et al, 2009) Available P on Surface X Runoff Precip. X Distribution Factor (Vadas et al., 2004, 2005, 2008) Dissolved P in Runoff All P not lost in runoff goes into soil
Dissolved and Sediment P Loss from Soil Dissolved Soil Runoff P = (Soil Labile P) (0.005) (Annual Runoff) Vadas et al. (2005) Sediment P Loss = (Eroded Sediment)(Soil Total P) (P Enrichment Ratio) Menzel et al. (1980) Sharpley (1980)
Soil Total P Jones et al. (1984) Sharpley et al. (1984) Organic P + Labile P + Active P + Stable P From OM From Mehlich-3 P From Labile P and PSP From Active P PSP P Sorption Parameter from soil OM, clay, Labile P (Vadas and White, 2010)
P Leaching out of topsoil P in Soil (mg/kg) MAX. (Nelson et al., 2005) Soil P = (a)(ln Leachate P) + b (Vadas, 2001) P concentration in leachate (mg/l)
P Leaching out of topsoil % precip. leaching through topsoil Nelson et al. (2005) Layer depth (inches)
Soil P changes over time Manure P 5% 95% Organic P Labile P Active P (100% fertilizer P) Distribute P based on PSP Stable P Two layers simulated within topsoil for P stratification P mixed between layers based on degree of mixing Crop P uptake from topsoil layers in proportion to relative soil P amounts
APLE Output
APLE P Loss and Soil P Evaluation For P loss, used measured data from 24 studies from 13 different states, Australia, and Ireland Used reported management data, measured soil P, runoff, erosion as inputs For soil P, used measured data from 19 studies Monitored changes in soil P from 1 to 25 years Used reported management data as inputs
APLE Soil P Validation
APLE P Loss Evaluation 30 Estimated P Loss (kg/ha) 25 20 15 10 5 0 y = 1.01x + 0.03 r² = 0.78 0 5 10 15 20 25 30 Measured P loss (kg/ha)
APLE 30 25 20 15 10 5 0 correct low high 0 5 10 15 20 25 30 Measured P loss APLE vs P Index 450 400 350 300 250 200 150 100 r 2 0.78 0.15 Correct 83% 53% Low 10% 11% High 7% 35% P Index 50 0 Low runoff, erosion high P application High erosion, low P application 0 5 10 15 20 25 30 Measured P loss
What is Proper Use for APLE?
Best use of APLE Appropriate Education about factors of P loss, in format that makes sense and is conceptually correct Directionally correct If I do X, will P loss go up or down? Quantitative uses Designed to estimate actual P loss Dynamic changes in P loss and soil P over time Specific sources and pathways of P loss Not Appropriate Event-based, spatial, beyond edge-of-field evaluations
Runoff P Loss (lb/ac) 10 8 6 4 2 Keeping P Loss Low Manure Soluble P Soil Soluble P Sediment P 0 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 1: 50 STP, 1 ton/ac erosion, 3 in runoff, 45 lb P/ac liquid on surface Case 2: 50 STP, 3 ton/ac erosion, 6 in runoff, 45 lb P/ac liquid tilled Case 3: 50 STP, 5 ton/ac erosion, 9 in runoff, 45 lb P/ac liquid tilled Case 4: 100 STP, 1 ton/ac erosion, 3 in runoff, 45 lb P/ac liquid on surface Case 5: 100 STP, 3 ton/ac erosion, 6 in runoff, 45 lb P/ac liquid tilled Case 6: 100 STP, 5 ton/ac erosion, 9 in runoff, 45 lb P/ac liquid tilled
Feeding Less P 0.5 % 0.3 % 3 ton/ac erosion 6 in runoff 45 lb P/ac liquid on surface 9% less P loss; 20% less soil P
Soil P Buildup and Decline Runoff P loss (lb/ac) P Loss in Runoff 3.50 3.00 2.50 2.00 1.50 1.00 0.50 Soluble P from Manure Soluble P from Soil Sediment P Mehlich 3 Soil P (ppm) 250 200 150 100 50 Mehlich 3 Soil P Top Layer Bottom Layer Whole Topsoil 1.5 ton/ac erosion 5 in runoff 45 lb P/ac No-till 0.00 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Year Year Runoff P loss (lb/ac) P Loss in Runoff 3.50 3.00 2.50 2.00 1.50 1.00 0.50 Mehlich 3 Soil P (ppm) 250 200 150 100 50 Mehlich 3 Soil P Manure applied (180 lb P/ac) and tilled once every 4 years 0.00 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Year Year
APLE Summary Attributes User-friendly, requires same inputs as P Index Represents most recent research in soil P, P loss algorithms Based entirely on research data, no professional judgment Easily accessed output on forms, source, quantity of P loss Rapid assessment of P loss for given management and transport scenarios Challenges Requires runoff and erosion as input
Current APLE Applications Since 2011, downloaded by >600 users in 48 states, 42 countries Integrated into widely-used watershed models to evaluate impact of agriculture on water quality (SWAT, EPIC, IFSM, Agro-IBIS, Chesapeake Bay Model) Incorporated into P-Indexes for WI, KY, OR, WA, MD, Canada
http://www.ars.usda.gov/services/docs.htm?docid=21763