1. Use of By-Plot CV’s for Refining Mid-Season Fertilizer N Rates Daryl Brian Arnall Plant and Soil Sciences Department Oklahoma State University

2. Introduction Scrutiny of Nitrogen Application Rise in Nitrogen cost Environmental impact Precision Nitrogen Application Great Potential Reduce Application Levels Use of Statistical Analysis for Improving Application Not Completely Examined Application Not Completely Examined

3. Objective Determine the relationship between the CV measured using spectral radiance measurements, and plant population at early growth stages. Determine the relationship between the CV measured using spectral radiance measurements, and plant population at early growth stages. Sensing direction in relation to the crop row direction impact on NDVI.

4. Method 25 plots at 3 locations: Plots measured 1.48m by 4.88m 3 nitrogen treatments implemented with each plot. 0 N, 120kg/ha Fall App., 80 kg/ha Top-dress

5. Plot Plan Check 0 N N-Rich 120 kg/ha N Fall App. Farmer Practice 80 kg/ha N Topdress

6. Method cont. At Feekes 1 (Emergence): Plots were established. Plots were established. Fall nitrogen applied. Fall nitrogen applied. Plant counts taken on 4 randomly selected rows. Plant counts taken on 4 randomly selected rows. At Feekes 6 (Stem Elongation): Topdress nitrogen applied Topdress nitrogen applied

7. Method cont. Sensing Began in January. Concluded at physiological maturity. Sensor held 75cm to 100 cm over the crop canopy. 3 seconds allowed for each reading.

8. Sensing Plan 5 Readings per trt: 2 with row, 2 across row, and 1 at a 45 degree to the seed row.

9. Sensing Plan

10. Method cont. At Physiological Maturity: A 1m 2 area hand harvested from each plot. Thrashed with a mechanical thrasher. Grain weighed for yield. Processed and analyzed for N content.

11. 2004 harvest

12. Results

13. CV and Population

14. CV over Time

15. RI Hybrid RI = Response Index RIharvest = Yield of N-rich plot / Yield of the check RIndvi = NDVI of N-rich plot / NDVI of check plot RIhybrid = NDVI of N-rich / ( NDVI of check plot / SqRt of the check plot CV )

16. Sensor Direction n = 3660 y = 0.98x + 0.01 R 2 = 0.97 n = 2325 y = 1.01x + 0.00 R 2 = 0.97

17. Directional CV

18. Conclusion High CV’s from sensor NDVI readings can be used as an indicator of poor plant stands. CV can be used to improve determination of RI. Seed row direction had no effect on NDVI Readings.

19. Questions?