An integrated study of nutrient leaching and greenhouse gas emissions
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An integrated study of nutrient leaching and greenhouse gas emissions. Tyson Ochsner and Rodney Venterea Soil and Water Management Research Unit Agricultural Research Service, USDA St. Paul, MN. The farm field as a system. Managed inputs: Crop rotation Fertilizer Tillage Etc.

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An integrated study of nutrient leaching and greenhouse gas emissions

Tyson Ochsner and Rodney Venterea

Soil and Water Management Research Unit

Agricultural Research Service, USDA

St. Paul, MN


The farm field as a system emissions

Managed inputs:

Crop rotation

Fertilizer

Tillage

Etc...

Soil biophysical

properties and

processes

Outputs:

Crop yield

GHG emissions

Nutrient leaching

Altered soil props

Etc...

Natural inputs:

Solar radiation

Precipitation

Temperature

Etc...

Alterations to management practices or biophysical processes typically affect more than one output of the system.


Overview of the r 3 experiment
Overview of the R emissions 3 experiment

  • Goal: Integrated assessment of yield, GHG emissions, nutrient leaching, and long-term changes in soil properties for various cropping practices

  • Setting:

    • Rosemount, MN (4445’ N, 9304’ W)

    • Waukegan silt loam (0.66 – 1.16 m deep)

    • 879 mm avg. annual precip; 6.4C annual mean temperature

  • Design:

    • Total of 39 large plots (76 m x 27 m)

    • 4 tillage practices, 3 crop rotations, 2 N sources, 3 replicates

  • Instrumentation:

    • Static chambers for GHG emission

    • Automated equilibrium tension lysimeters for drainage and leaching

    • CS616 water content sensors

    • Cu-constantan thermocouples

    • Tipping bucket rain gauges

    • 3 comprehensive weather stations within 2 km


Management contrasts
Management contrasts emissions

  • Continuous corn vs. corn/soybean

    • US corn acreage projected up 10 million acres by 2010

    • “... new corn acreage will come from shifts in crop rotation from soybeans to corn.” C.E. Hart, Iowa Ag Review, Fall 2006

  • Urea vs. anhydrous ammonia

    • Domestic N production declining; imports rising

    • Urea easier and safer to store, handle, and transport


2005 2006 weather

Temperatures at or slightly above average emissions

June and July rainfall 25% < average in 2005

50% < average in 2006

2005 – 2006 weather


2006 soil water storage

Greater moisture depletion under corn emissions

Deeper freeze, later thaw under soybean residue

2006 soil water storage


2006 soil nh 4 concentrations
2006 soil NH emissions 4 concentrations


2006 soil ph
2006 soil pH emissions


2005 2006 crop yields
2005 – 2006 crop yields emissions

  • Continuous corn resulted in ~15% yield reduction relative to corn/soybean rotation with equal N fertilizer (135 kg ha-1)

  • Urea produced higher corn yields, but not statistically significant

  • No carryover effect of N source on soybean yield

n = 6, means followed by the same letter are not significantly different at the p<0.05 level


Nitrate leaching may 2005 oct 2006
Nitrate leaching emissions May 2005 – Oct. 2006

n = 2, no significant differences at p < 0.1 level


Cumulative growing season n 2 o emissions may 2005 oct 2006
Cumulative growing season N emissions 2O emissionsMay 2005 – Oct. 2006

  • Mass of N loss relatively small

  • C/C rotation resulted in larger fluxes than C/S

  • AA resulted in larger fluxes than U

  • Switching from AA to U like saving 0.2 - 0.6 t SOC ha-1 yr-1.


Nitrogen balance may 2005 oct 2006
Nitrogen balance emissions May 2005 – Oct. 2006


Tentative conclusions
Tentative conclusions emissions

  • Previous crop can affect soil freezing and thawing with implications for GHG emissions and nutrient leaching.

  • The trend toward replacement of AA with urea may reduce N2O emission without adversely affecting yield or nitrate leaching.

  • 15% yield penalty for continuous corn and increased N2O emission.

  • N balance suggests that the C/S rotation promotes greater mineralization of SOM than the C/C rotation.


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