modeling phosphorus movement
DESCRIPTION
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.TRANSCRIPT
Peter Vadas
USDA-ARS, Dairy Forage Research Center, Madison, WI
Current Models for Phosphorus Loss from Agricultural Systems
Agricultural P Loss? It Depends
How do we effectively integrate decades of data and multiple processes into comprehensive method producers, policy makers can use to
make decisions?
Soil P quantity and chemistry
P Application rate and method
Manure and fertilizer chemistry
Runoff hydrology
Erosion
How much does agriculture contribute to P pollution? What can producers do to decrease P
loss? How do we answer these questions?
The Case for Models Due to sheer number of important physical and
management interactions, impossible to meet demands for information fast enough and cheap enough relying on field research alone.
Models are effective, efficient way to integrate variety of field data to make decisions. Some scenarios (climate change, system integration) impossible to address without models.
Model development forces us to formalize and test understanding of natural processes, and thus identify knowledge and data gaps.
Models are simple representations of our understanding of reality. Can’t capture all complexities, what we don’t know.
Current P Model Options
Complex Simple
SWAT
APEX
AnnAGNPS
P Index
User friendly,
quantitativeAPLE
WI SNAP+
OK PPM
TX TBET
Complex P Models
Daily time-step, field to watershed scale, quantitative predictions; For TMDL-type projects
Process-based, spatially explicit simulations of hydrology, multiple contaminant transport through landscape
Data intensive for inputs and testing, extensive user experience and skill needed
Should be calibrated
Require dedicated support system for updating and development
Simple P Indexes
Annual time-step, field scale, relative ranking of risk of P loss
Good for producer/policy education
Not data intensive, little user experience and skill needed, no calibration needed
Not process-based, calculations based on data and professional judgment
Generally had little field testing to verify accuracy of predictions and recommendations
User-friendly, Quantitative P Loss
Models Models that estimate (lb/ac) annual, field-scale, P loss
Moderate data requirements (mix of databases and user-defined management)
Require moderate user experience and skill, no calibration needed
Process-based equations based only on experimental data, not spatially explicit
Able to test with widely available P loss data
Excel spreadsheet model that estimates (lb/ac) annual, field-scale, dissolved and sediment P loss in surface runoff for given set of management, soil P, erosion, runoff conditions.
Intended to be process-based like SWAT, APEX, but user-friendly like P Index.
APLE Inputs
APLE Inputs
APLE Output
APLE Testing
P loss in runoff - Measured data from 28 crop studies from 13 states, Australia, Ireland (Vadas et al., JEQ 2009), 14 grazing studies from 5 states, Australia, New Zealand (unpublished)
Soil P dynamics - Measured data from 19 studies monitoring changes in soil P from 1 to 25 years (Vadas et al., JEQ 2012)
Current updates include P loss from barnyards and feedlots, uncertainty estimates
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 tilled
Keeping P Loss Low
Feeding Less P0.5 % 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
1.5 ton/ac erosion5 in runoff45 lb P/ac
No-till
Manure applied (180 lb P/ac) and tilled once every 4 years
Summary
Models are effective way to integrate years of P research data to meet demand for management and impact information fast and cheap.
Models vary in complexity and appropriate uses, not always easy to know which one to choose and how to use output.
New P models help capture current science, balance versatility and complexity with user-friendliness
Models are indispensible; need to be well developed and tested, have committed support from policy makers, scientists
