toby ahrens 26 oct 2004 linking spatial variability of soil n retention mechanisms to...
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![Page 1: Toby Ahrens 26 Oct 2004 Linking Spatial Variability of Soil N Retention Mechanisms to Landscape-level Fates in Yaqui Valley, Mexico](https://reader030.vdocuments.net/reader030/viewer/2022032522/56649d6c5503460f94a4c512/html5/thumbnails/1.jpg)
Toby Ahrens
26 Oct 2004
Linking Spatial Variability of Soil N Retention Mechanisms to
Landscape-level Fates in Yaqui Valley, Mexico
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Goals
Quantify degrees of N contamination under different management regimes
Investigate the value of spatial data sets varying in resolution
Integrate 10+ yrs of biogeochemistry research in the Valley
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What do I need to do to get there?
Link process and transport models
Improve process models Include abiotic retention mechanisms
Develop spatial data sets Eg. soil type, texture, mineralogy,
management, leaching potential
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Coastal eutrophication
Declassified Keyhole satellite image
March 8, 1978
(Thanks Mike!)
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Nitrate-contaminated groundwater
<10 ppm10-40 ppm116 ppm
Hungate, unpublished data, 1997-98
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Two Q’s guiding my efforts:
1. What soil characteristics control N availability, retention and loss in OM-deficient ag soils?
2. Can the spatial variability of these characteristics be linked to aqueous N fates throughout the Valley?
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Model schematic…
soil properties
NLOSS
soil mineralogy
crop yield (+N use)
Solute transport
un/saturated boundary conditions
management unit
crop type
Output maps:• Leaching vulnerability• Aquifer contamination• Coastal N sources
groundwater depth
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Lee Addams’s modelIrrigation Drains Irrigation Losses Main Canal Infiltration
250m-1km
“AQUIFER HORIZON”
“CONNECTOR HORIZON”
“SHALLOW HORIZON”
WellScreens
Irrigation Drains Irrigation Losses Main Canal Infiltration
250m-1km
“AQUIFER HORIZON”
“CONNECTOR HORIZON”
“SHALLOW HORIZON”
WellScreens
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Major modeling efforts:
Soil submodel including sorption isotherms and mineral fixation
Solute transport component to saturated hydrology model
Saturated/unsaturated boundary layer conditions
Spatial data referencing
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Applied N:250 kg/ha
Plant uptake:31%
Leached:2-5%
(14-26%)
Gaseous losses:
NO+N2O: 2-5%NH3: __%N2: __%
?
?
?
?
Drainage canals:NO3
- + NH4+: 2-5%
NO+N2O: <0.1%
References:
Riley et al. 2001Harrison 2003Matson et al. 1998Ortiz-Monasterio, pers. comm.
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Applied N:250 kg/ha
Plant uptake:31%
Leached:2-5%
(14-26%)
Gaseous losses:
NO+N2O: 2-5%NH3: __%N2: __%
?
?
?
?
Drainage canals:NO3
- + NH4+: 2-5%
NO+N2O: <0.1%
Field experiments:
• abiotic fixation
• link leaching potential to actual fates
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Future directions and broader implications…
Does better spatial resolution increase our ability to predict SW/GW vulnerability? And the degree of how mechanistic submodels
are?
Identify thresholds for N retention Or pesticides…
Investigate management scenarios Different irrigation or fertilization regimes
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Resolution of input data:Field based…
Legend
ARCILLA
5.820000 - 27.820000
27.820001 - 38.940000
38.940001 - 49.300000
49.300001 - 59.460000
59.460001 - 87.300000
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Legend
ARCILLA
5.820000 - 27.820000
27.820001 - 38.940000
38.940001 - 49.300000
49.300001 - 59.460000
59.460001 - 87.300000
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Policy implications
The Danish and Dutch experiences: N control policies aimed at reducing N
leaching (SW + GW) and NH3 and N2O emissions
Importance of model validation