1. Within Field Variation in Corn Response to N Fred Below Department of Crop Sciences University of Illinois at Urbana-Champaign

2. The Team

3. North South Average yield (bu acre -1 ) 190 170 165 160 155 150 145 130 >120 Maurer 2002 Yield map

4. Prerequisites for Variable Rate N Areas of differing N response Easily identify variable areas Improve yield/reduce N use

5. Objective Determine the degree of variability within individual fields in their responsiveness to fertilizer N

6. Four farm fields near Beardstown, IL FieldAreaHybrid acres Allen 87P 31N27 Wilkey 60P 34H31 Maurer North 80P 34H31 Maurer South 80P 31N27

7. N treatments at Wilkey 0 100 150 200 300 N rate (lb acre -1 )

8. 1 2 3 4 5 6 7 8 9 10 0 100 150 200 300 N rate (lb acre -1 ) Sampling regions at Wilkey

9. Grain yield N rate (lb acre -1 ) Grain yield (bu acre -1 )

10. Grain yield (bu acre -1 ) at Maurer South

11. Grain yield N rate (lb acre -1 ) Grain yield (bu acre -1 )

12. Grain yield (bu acre -1 ) at Wilkey 400 Feet0 200

13. Grain protein (%) 400 Feet0 200 Wilkey

14. Grain yield (bu acre -1 ) 400 Feet0 200 Wilkey

15. Individual kernel weight (mg) 400 Feet0 200 Wilkey

16. Kernel number (no. m -2 ) 400 Feet0 200 Wilkey

17. What component drives yield Grain yield (bu acre -1 ) Kernel number (number m -2 ) Kernel weight (mg)

18. Conclusions Differing yield response to N within Farmers’ fields Variable applied N results in differing N availability Sink-driven yield response to N is a challenge for VRN