Reconciling Model Parameters for P with Field Measurements

Transcription

1 Reconciling Model arameters for with Field Measurements eter Vadas USDA-ARS Dairy Forage Research Center Dairy Forage Research Center

2 Original EIC Model Development Jones, C.A., C.V. Cole, A.N. Sharpley, and J.R. Williams A Simplified Soil and lant hosphorus Model.1. Documentation. Soil Sci. Soc. Am. J. 48: Sharpley, A.N., C.A. Jones, C. Gray, and C.V. Cole A Simplified Soil and lant hosphorus Model.2. rediction of Labile, Organic, and Sorbed hosphorus. Soil Sci. Soc. Am. J. 48: Jones, C. A., A. N. Sharpley, and J. R. Williams A simplified soil and plant phosphorus model: III. Testing. Soil Sci. Soc. Am. J. 48: Sharpley, A. N., U. Singh, G. Uehara, and J. Kimble Modeling Soil and lant hosphorus Dynamics in Calcareous and Highly Weathered Soils. Soil Sci. Soc. Am. J. 53:

3 Common Soil Routines Inputs Runoff Dissolved, Leaching, Crop Uptake Organic Labile Active Stable Soil Total for Sediment Loss Make sure pool sizes are simulated well to feed pathways Good initialization Good dynamics as soil changes though time Make sure loss is simulated well as a function of pool sizes

4 ool Initialization Organic Labile S Active 4x Stable Labile :Active = S: (1-S) Stable = 4 x Active Organic = OC / 14 / 8 Sum of pools = soil Total Need to estimate Labile, S, check that sum of pools is good estimate of soil total

5 Initializing Labile Labile Originally measured for EIC with anion exchange membranes represents dissolved in solution and easily desorbed from soil AE- typically less than common ST amounts, probably more variable Correlated to measured ST so it can be initialized from available data Original EIC relationships different from later ones (underestimate labile ) maybe due to data set with relatively low soil Now, estimate labile as 0.5 of Bray-1, Mehlich-3; equal to Olsen and Mehlich 1 Be careful with high ph or calcareous soils with different chemistry

6 Initializing S S Originally experimentally measured for EIC Measure labile, incubate soil with added for 6 months, re-measure labile S = % of added that remains as labile Correlate S to commonly measured soil properties (clay, OM, labile ) Measuring S introduces same variability as with measuring labile as AE-, same original data set

7 Testing Initialization Do EIC equations to estimate Labile and S initialize pools well enough so estimated total correlates with measured total? Estimate Labile from ST 0.5 x Mehlich 3, Bray x Olsen, Mehlich 1 Estimate S from soil properties (clay, OM, Labile ) from EIC Estimate total as sum of pools and compare with measured total Vadas,.A., and M.J. White Validating soil phosphorus routines in the SWAT Model. Trans. ASABE. 53: Dairy Forage Research Center

8 Estimated Total (mg/kg) Testing Initialization y = 0.70x R² = 0.75 n= Measured Total (mg/kg) Older versions of SWAT may not include Labile with sum of pools, which will underestimate total even more EIC equations may estimate less Labile from ST, resulting in even less total Dairy Forage Research Center

9 New equations for S Estimate Labile from ST 0.5 x Mehlich 3, Bray x Olsen, Mehlich 1 Use measured ST and total to calculate S Total = Labile + 5(1-S x Labile )/(S) Relate calculated S (not measured) to soil properties (clay, OM, Labile ) Use soil properties, ST to estimate pools and total as sum of pools, compare to measured total Vadas,.A., and M.J. White Validating soil phosphorus routines in the SWAT Model. Trans. ASABE. 53: Dairy Forage Research Center

10 Estimated Total (mg/kg) Testing new Initialization y = 1.02x R² = Measured Total (mg/kg) Dairy Forage Research Center

11 Implications New approach estimates lower S from same soil properties, which means greater Active, Stable, Total SWAT default of 0.4 for S may be much too high for many soils, resulting in too little Total Too little Total = underestimation of sediment loss in erosion, having to unrealistically set parameters for calibration S needs to be dynamic in model (increases as labile increases) so more remains as Labile as soil increases Bolster, C.H., and.a. Vadas Comparison of two methods for calculating the sorption capacity parameter in soils. Soil Sci. Soc. Am. J. 82: Dairy Forage Research Center

12 Soil Dynamics Over Time Organic Labile S Active Stable As soil changes ( additions, crop uptake, loss), need to move between pools to maintain correct amount so availability is correct for new loss or uptake When Labile or Active relatively too big, calculate imbalance and move 0.1 of imbalance per day older versions of SWAT had errors in absence of 0.1 from Labile to Active. Similar process between Active and Stable, coefficient of

13 Testing Soil Dynamics How do we test reliability of simulation? 1. Changes in simulated Labile and total over time should correlate with measured changes in both (Labile :ST relation maintained) 2. Simulated loss (dissolved, sediment ) should correlate with measured loss at field scale Use both tests to see if routines are robust and reliable Dairy Forage Research Center

14 Estimated Total (mg/kg) Changes in Total over time Measured data from 9 studies monitoring changes in total from 4 to 25 years y = 1.00x R² = 0.97 n= Measured Total (mg/kg) Vadas,.A., B.C. Joern, and.a. Moore, Jr Simulating soil phosphorus dynamics for a phosphorus loss quantification tool. J. Environ. Qual. 41:

15 Estimated Soil (mg/kg) Changes in ST over time Measured data from 20 studies monitoring changes in soil from 1 to 25 years y = 1.04x R² = 0.93 n= Measured ST (Mehlich 3 - mg/kg) Vadas,.A., B.C. Joern, and.a. Moore, Jr Simulating soil phosphorus dynamics for a phosphorus loss quantification tool. J. Environ. Qual. 41: Vadas,.A., N.M. Fiorellino, F.J. Coale, R. Kratochvil, A.S. Mulkey, and J.M. McGrath Estimating legacy soil phosphorus impacts on phosphorus loss in the Chesapeake Bay watershed. J. Environ. Qual. 47:

16 Dissolved loss in Runoff Runoff Dissolved Organic Labile S Active Stable Dissolved runoff = Labile x Runoff x Kd Sediment runoff = Total x erosion x ER Menzel et al. (1980) Sharpley (1980)

17 Runoff Dissolved (mg/l) Estimating Dissolved Loss y = 0.002x R² = Similar to SWAT default of 175 for K d Soil Test (Mehlich 3 or Bray 1 - mg/kg) Vadas,.A.,.J.A. Kleinman, and A.N. Sharpley Relating soil phosphorus to dissolved phosphorus in runoff: A single extraction coefficient for water quality modeling. J. Environ. Qual. 34:

18 Estimated T Loss (kg/ha) Estimating Total Loss Measured data from 28 studies from 13 different states, Australia, Ireland y = 1.03 x 0.03 r² = Measured T loss (kg/ha) Vadas,.A., L.W. Good,.A. Moore Jr., and N. Widman Estimating phosphorus loss in runoff from manure and fertilizer for a phosphorus loss quantification tool. J. Environ. Qual. 38:

19 Implications With S, Labile estimated well, and dynamic S, EIC equations for soil dynamics, loss are robust and reliable In older versions of SWAT, no 0.1 factor when moving from Labile to Active. Result is that all added inorganic moved immediately to Active and slowly moves back to Labile. This is opposite to what really happens and will underestimate dissolved loss, especially for surface application. Dynamics coefficients instead of 0.1 are an option too, with somewhat improved simulations Inputs Organic Labile 0.1 Active Stable Vadas,.A., T. Krogstad, and A.N. Sharpley Modeling phosphorus transfer between labile and non-labile soil pools: updating the EIC model. Soil Sci. Soc. Am. J. 70:

20 Logic of Soil Routines Initialize Labile from measured ST Initialize S from measured soil properties (OM, clay, Labile ) Initialize Organic from measured OM Model uses S to initialize Active and Stable, estimates Total as sum of pools Model tracks changes in pool sizes over time based on S, imbalance coefficients Model estimates loss based on Labile and total Use multiple tests for simulation ST and total dynamics, dissolved and sediment loss, leaching, crop uptake Dairy Forage Research Center

21 Dissolved Loss from Surface Manure, Fertilizer applied - into soil from tillage, liquid manure infiltration on surface X Availability factor Fertilizer: 100% Manure: % WE Available on Surface X Runoff recip. X Distribution Factor Dissolved in Runoff All not lost in runoff goes into soil, track changes in available surface through time Collick A.S., T.L. Veith, D.R. Fuka,.J.A. Kleinman, A.R. Buda, J.L. Weld, R.B. Bryant,.A. Vadas, M.J. White, R.D. Harmel, and Z.M. Easton Improved Simulation of Edaphic and Manure hosphorus Loss in SWAT. J. Environ. Qual. 45: Vadas,.A., W.J. Gburek, A.N. Sharpley,.J.A. Kleinman,.A. Moore, Jr., M.L. Cabrera, and R.D. Harmel A model for phosphorus transformation and runoff loss for surface-applied manures. J. Environ. Qual. 36: Vadas,.A., L. Owens, and A.N. Sharpley An empirical model for dissolved phosphorus in runoff from surface-applied fertilizers. Agric. Ecosys. Environ. 127: Dairy Forage Research Center

22 Questions??