1. Tastes Great. Less Filling
Tastes Great! Less Filling! Comparing Algorithms for Nitrogen Management
August 5, 2009
4/7/2019
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
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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
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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
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5. Sufficiency Approach
Relationship between response index measured at harvest (using control plot) and AONR from regional project
Linear Plateau
Y = x –
r2=0.70 Joint = 1.6 Plat = 162
Quad Plateau
Y = -99.5x x – 335.3
r2=0.71 Joint = 2.3 Plat = 180
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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)
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7. Sufficiency Approach Sensor approaches alone do not work very well
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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
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9. Sufficiency Approach Not as good with new data Linear Y = -1.6x + 2.8
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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
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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?
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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)
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13. Spatial Application
N rec as a function of NDVI
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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
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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)
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16. Yield Prediction New upper bound representing real “potential”
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17. Yield Prediction
Data from Regional Project
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18. Yield Prediction
Yield goal or yield potential is not a very good predictor of nitrogen rate by itself (78 sites)
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19. Response Alone
Response alone is also not necessarily a good predictor (same 78 sites)
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20. Response Alone
If we calculate response with the 40 lb N/acre yield in the denominator (same 78 sites)
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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
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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
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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
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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
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NUE Meeting

25. X = 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
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26. - = Easier to Read GNUP-YPN GNUP-YP0 NUE Fertilizer rec 4/7/2019
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27. Nitrogen Use Efficiency
How is nitrogen use efficiency determined?
Arbitrarily?
Based upon several site-years worth of data in Ohio
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28. Spatial Application
N rec as a function of NDVI
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29. Imposed Assumptions Some yield-goal based algorithms have limits
Maximum attainable yield
Maximum N application rate
Minimum N application rate
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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)
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31. Conclusions Similarities Differences Challenges
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
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32. Change in Nitrogen Need by Year
Data from NW Ohio – corn after beans
Year
Opt. N
Yield
1998
187
239
1999
160
184
2000a
170
157
2000b
149
153
2001
233
189
2002
169 89
2003
218
237
2004
162
193
2005
175
204
Avg
181
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33. Thanks!!!
Questions?
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NUE Meeting