1. Variability in Corn Response to N Fertilizer along a 1000-ft Hillslope
John Schmidt
Nan Hong
Adam Dellinger
Doug Beegle
Henry Lin
ARS
Missouri
Penn State

2. Background Improving N recommendations for corn
Spatial variability in relief, aspect, soil water content
Fox observed a relationship in PA between EONR and July precipitation

3. Field site - 2005 1000 ft horizontal, 30 ft vertical relief
Previous crop soybean
Soil pH: 5.3 – 5.7
Soil P (M3): 24 – 77
Soil K (M3): 97 – 156

4. Field site – relief and plot locations

5. Treatment design Ten locations, 2 blocks each
Six N treatments: 0, 50, 100, 150, 200, 250 lb N / acre, applied at planting as NH4NO3
TDR access tubes at each location
Soil water content, 5 June – 2 Sept, – 90 cm depth
Canopy reflectance, Crop Circle ACS-210
Grain yield at harvest

6. Rainfall and soil water content

7. Grain yield response

8. EONR (Economic Optimum N Rate)

9. N rec’s as a function of yield goal?

10. Soil water content

11. Grain yield related to soil water content

12. EONR related to soil water content

13. July 01 sensor information

14. Summary
EONR increased linearly with an increase in soil profile water content, 25 July – 30 June
EONR was not correlated to NDVI ratio
NDVI 01 July decreased linearly with increasing soil profile water content on 30 June