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Tastes Great! Less Filling! Comparing Algorithms for Nitrogen Management

This presentation discusses the conceptual differences and similarities between sufficiency-based and yield potential-based approaches for identifying the optimum N rate using optical sensors. It presents data to evaluate each approach and shares the challenges of each algorithm.

robertgagnon
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Tastes Great! Less Filling! Comparing Algorithms for Nitrogen Management

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  1. Tastes Great! Less Filling! Comparing Algorithms for Nitrogen Management August 5, 2009 NUE Meeting

  2. Overview • Currently there are two lines of thinking as it relates to identifying the optimum N rate using optical sensors • Response based (synonymous with sufficiency approach) • Yield potential and response based • The goal of this presentation is to discuss conceptual differences and similarities, present some data to evaluate each approach, and to share challenges of each NUE Meeting

  3. Sufficiency Approach • Actually utilized by both approaches • Measurement of response to N using a reference/nitrogen rich strip and some corresponding lower N rate strip • Sufficiency approach uses estimate of responsiveness to identify N recommendation NUE Meeting

  4. Sufficiency Approach • Some use a linear model • Regional SPAD algorithm (Scharf et al., 2006) • MO algorithm (Kitchen, personal communication) • Others use more sophisticated models • NE SPAD and active sensor algorithm (Varvel et al., 2007; Fernando Solari dissertation work) • Use average N response curve and determine N rec based upon sufficiency level • Following is an example of the sufficiency approach NUE Meeting

  5. Sufficiency Approach • Relationship between response index measured at harvest (using control plot) and AONR from regional project Linear Plateau Y = 225.51 x – 204.19 r2=0.70 Joint = 1.6 Plat = 162 Quad Plateau Y = -99.5x2 + 456.2x – 335.3 r2=0.71 Joint = 2.3 Plat = 180 NUE Meeting

  6. Sufficiency Approach • Still need to convert from RI measured at harvest to RI measured in-season using an optical sensor (relationship between in-season RI and optimum N is not very good) NUE Meeting

  7. Sufficiency Approach • Sensor approaches alone do not work very well NUE Meeting

  8. Sufficiency Approach • Relationship between in-season RI and RI harvest (did look good originally prior to 2007) Linear Y = -1.6x + 2.7 r2=0.74 NUE Meeting

  9. Sufficiency Approach • Not as good with new data Linear Y = -1.6x + 2.8 r2=0.29 NUE Meeting

  10. Sufficiency Approach • Should the sufficiency approach be the same across all growth stages? • Good question • Is RI (SI) stable over time? • Does a higher RI (lower SI) at an earlier growth stage translate into higher fertilizer rates? • The MO and NE algorithms do have different recommendations, but they are only segregated into two general growth stages less than and greater than 8 or 10, respectively NUE Meeting

  11. Sufficiency Approach • Empirically based approach that uses only an estimate of response (sufficiency) to determine N recommendation • Post harvest estimates of RI are well correlated with AONR • Estimating in-season RI (SI) is still a concern • This is also a concern with the yield-goal based approach • Should the check plot be used to more accurately identify RI? NUE Meeting

  12. Sufficiency Approach • I am not sure how this is applied spatially across the landscape • E.g. – Once an RI (SI) is calculated for a field, how is altered spatially across the landscape to adjust spatial N application rates? • As an outsider looking in, assumption must be that response changes spatially (I would agree, but so does everything else) NUE Meeting

  13. Spatial Application • N rec as a function of NDVI NUE Meeting

  14. Yield Goal Based Approach • More mechanistic than the sufficiency-based approach • Includes an estimate of both yield potential from a sensor measurement (and a model), and an estimate of response NUE Meeting

  15. Yield Prediction • With the realization that the bulk of these sensor measurements are made prior to V10, it is not surprising that things can and do change from the sensing date to full maturity • So instead of focusing on predicting the average exponential function of the data, what if we focus on the upper bound that represents real “potential” (assuming things continue on has they have been) NUE Meeting

  16. Yield Prediction • New upper bound representing real “potential” NUE Meeting

  17. Yield Prediction • Data from Regional Project NUE Meeting

  18. Yield Prediction • Yield goal or yield potential is not a very good predictor of nitrogen rate by itself (78 sites) NUE Meeting

  19. Response Alone • Response alone is also not necessarily a good predictor (same 78 sites) NUE Meeting

  20. Response Alone • If we calculate response with the 40 lb N/acre yield in the denominator (same 78 sites) NUE Meeting

  21. Yield Goal Based Approach • Current adjustment of in-season RI (using check) to harvest RI (prior to 2007) Linear Y = -1.6x + 2.7 r2=0.74 NUE Meeting

  22. Yield Goal Based Approach • Current adjustment of in-season RI (using target) to harvest RI (prior to 2007) Linear Y = -1.8x + 3.0 r2=0.39 NUE Meeting

  23. Yield Goal Based Approach • Same issue with current estimate of RI as we discussed with sufficiency approach • Estimate of RI harvest has gotten worse with new data • Not sure what to do at this point NUE Meeting

  24. Yield Goal Based Approach • At this point we have an estimate of yield potential, and an estimate of response • We calculate the grain N uptake of at the yield potential without additional N • Multiply that value by the adjusted RI • We now have the new grain N uptake at the new achievable yield level • To calculate the N rec, subtract the grain N uptake at the original yield potential from the grain N uptake at the new yield potential NUE Meeting

  25. Easier to Read Grain N Uptake (GNUP-YPN) = YPN x grain N Grain N Uptake (GNUP-YP0) = YP0 x grain N = X RI (after linear adjustment) YP0 Current yield potential without additional fertilizer YPN Yield potential with additional fertilizer NUE Meeting

  26. Easier to Read - GNUP-YPN GNUP-YP0 = NUE Fertilizer rec NUE Meeting

  27. Nitrogen Use Efficiency • How is nitrogen use efficiency determined? • Arbitrarily? • Based upon several site-years worth of data in Ohio NUE Meeting

  28. Spatial Application • N rec as a function of NDVI NUE Meeting

  29. Imposed Assumptions • Some yield-goal based algorithms have limits • Maximum attainable yield • Maximum N application rate • Minimum N application rate NUE Meeting

  30. Yield Goal Based Algorithms • Spatial application is made based upon variations in yield potential estimates from sensor readings and a static response estimate (this is not necessarily true for all yield goal based algorithms) NUE Meeting

  31. Conclusions • Similarities • Use of reference strip & subsequent measurement of response/sufficiency • Differences • How N is applied spatially • Sufficiency approach – response is variable • Yield-based approach – yield potential is variable (response could be variable) • Challenges • Better prediction of in-season responsiveness NUE Meeting

  32. Change in Nitrogen Need by Year • Data from NW Ohio – corn after beans NUE Meeting

  33. Thanks!!! • Questions? NUE Meeting

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