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In-Season Nitrogen Fertilization Based on Sensor-Estimated Potential Yield

In-Season Nitrogen Fertilization Based on Sensor-Estimated Potential Yield. E.V. Lukina, K.W. Freeman,K.J. Wynn, W.E. Thomason, G.V. Johnson, M.L. Stone, J.B. Solie, W.R. Raun. Oklahoma State University Department of Plant and Soil Sciences. Introduction.

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In-Season Nitrogen Fertilization Based on Sensor-Estimated Potential Yield

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  1. In-Season Nitrogen Fertilization Based on Sensor-Estimated Potential Yield E.V. Lukina, K.W. Freeman,K.J. Wynn, W.E. Thomason, G.V. Johnson, M.L. Stone, J.B. Solie, W.R. Raun Oklahoma State University Department of Plant and Soil Sciences

  2. Introduction • Low nitrogen use efficiency for cereal production (33%) • In-season reflectance readings from wheat at high resolutions (1m2) have been shown to be highly correlated with biomass • Our present focus has been to apply N rates to each 1m2 area based on predicted potential yield • Potential grain yield: yield predicted for a given year and site, based on the assumption that the level of growth factors responsible for early stages of development of the crop will be maintained (limitations that existed at early stages of growth will continue to similarly influence development to maturity, e.g., N deficiency)

  3. Objective • To investigate the potential for N fertilization using in-season estimates of potential yield for every 1m2 based on plant reflectance readings

  4. Materials and Methods • Winter wheat Coker, Custer, and 7853 • Experimental design • Randomized complete block • Four replications • 4m x 7m plots • 1m2 subplots for variable rate treatments • Spectral reflectance readings at 671nm (red) and 780nm (near infrared) taken at Feekes physiological growth stages 4 and 5

  5. Optical sensor developed by OSU

  6. Materials and Methods • NDVI (Normalized Difference Vegetation Index) calculated for each subplot (1m2) by the equation (NIR-Red)/(NIR+Red) • For two of the treatments, N rates were determined based on tissue N need at F4 and F5, respectively • For the yield potential treatment, N rates were determined based on EY (estimated yield) index: EY=(NDVIF4+NDVIF5)/GDD GDD=(Tmin+Tmax)/2- 4.4 °C

  7. Materials and Methods • Ammonium nitrate applied after sensing in early March (March 6-13) • Plots harvested by treatment (4m x 7m) in mid June • Grain weight and percent moisture automatically recorded • Total N in grain samples analyzed by dry combustion (Schepers et al., 1989)

  8. Covington Feekes5 NDVI Contour Map 0.80 0.76 0.72 0.68 0.64 0.60 0.56 0.52 0.48 0.44 0.40 0.36 0.32 0.28 0.24 Spatial variability

  9. Results • Due to weed problems and high soil test N, one field experiment in 1998-99 did not respond to N fertilizer • Grain yield and N fertilizer requirement were highly correlated with yield potential-based N fertilization for both years at both locations. • Grain yield, N uptake and NUE were increased using EY compared to fixed rates in 1999, while the next year results were not consistent with the first year of study.

  10. Results • The highest grain yield and N uptake during the second year of experiment was obtained on the plots with fixed N rate of 90 kg N per ha. • The highest NUE’s were observed on the yield potential-based N fertilization plots at Morrison location, and 45 kg of N per ha (fixed rate) at Covington.

  11. Grain yield response to N rates,Covington, 1999

  12. Grain yield response to N rates,Covington, 2000

  13. Grain yield response to N rates,Morrison, 2000

  14. N fertilizer requirement as influenced by N rates, Covington, 1999

  15. N fertilizer requirement as influenced by N rates, Covington, 2000

  16. N fertilizer requirement as influenced by N rates, Morrison, 2000

  17. Grain yield response to Treatment

  18. Grain yield response to Treatment YP1 (based on 98, 99, 00 forage N uptake data)YP2 (based on 00 N uptake data only)

  19. N uptake response to Treatment

  20. N uptake response to Treatment

  21. NUE response to Treatment

  22. NUE response to Treatment

  23. Conclusion • EY may be used as a predictor of potential yield and for adjustment of in-season N fertilization rates • Yield potential-based in-season N fertilization may increase grain yield, N uptake and NUE

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