An integrated study of nutrient leaching and greenhouse gas emissions

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. The farm field as a system 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.

3. Overview of the R3 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. Temperatures at or slightly above average June and July rainfall 25% < average in 2005 50% < average in 2006 2005 – 2006 weather

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

7. 2006 soil NH4 concentrations

8. 2006 soil pH

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

10. Nitrate leachingMay 2005 – Oct. 2006 n = 2, no significant differences at p < 0.1 level

11. Cumulative growing season N2O 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.

12. Nitrogen balanceMay 2005 – Oct. 2006

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 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.