1. 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

2. Soil biophysical properties and processes Outputs: Crop yield GHG emissions Nutrient leaching Altered soil props Etc... Managed inputs: Crop rotation Fertilizer Tillage Etc... Natural inputs: Solar radiation Precipitation Temperature Etc... The farm field as a system Alterations to management practices or biophysical processes typically affect more than one output of the system.

3. Overview of the R 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

4. Management contrasts 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

5. 2005 – 2006 weather Temperatures at or slightly above average June and July rainfall 25% < average in 2005 50% < average in 2006

6. 2006 soil water storage Greater moisture depletion under corn Deeper freeze, later thaw under soybean residue

7. 2006 soil NH 4 concentrations

8. 2006 soil pH

9. TreatmentCornSoybean ---- Mg ha -1 ----- C/C AA7.66 a n/a C/C U8.26 a n/a C/S AA8.89 b 2.71 c C/S U9.73 b 2.77 c n = 6, means followed by the same letter are not significantly different at the p<0.05 level 2005 – 2006 crop yields 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

10. TreatmentDrainage NO 3 -N conc. NO 3 -N load mmmg L -1 kg ha -1 yr -1 C/C AA2639.729 C/S AA20428.567 C/S U12830.248 n = 2, no significant differences at p < 0.1 level Nitrate leaching May 2005 – Oct. 2006

11. Treatment N 2 O emission Equivalent mass of soil C loss kg ha -1 yr -1 C/C AA3.1789 C/C U0.56143 C/S AA0.9229 C/S U0.251 Cumulative growing season N 2 O emissions May 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.

12. Nitrogen balance May 2005 – Oct. 2006 IMPORTEXPORTSDIFF TreatmentFertilizer NO 3 -N leached N 2 O-N emissions Grain N removal kg ha -1 yr -1 C/C AA135293.1117-14 C/S AA67.5670.9159-159 C/S U67.5480.2168-149

13. Tentative conclusions 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 N 2 O emission without adversely affecting yield or nitrate leaching. 15% yield penalty for continuous corn and increased N 2 O emission. N balance suggests that the C/S rotation promotes greater mineralization of SOM than the C/C rotation.