Tastes Great. Less Filling Tastes Great! Less Filling! Comparing Algorithms for Nitrogen Management August 5, 2009 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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) 4/7/2019 NUE Meeting

Sufficiency Approach Sensor approaches alone do not work very well 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

Sufficiency Approach Not as good with new data Linear Y = -1.6x + 2.8 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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? 4/7/2019 NUE Meeting

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) 4/7/2019 NUE Meeting

Spatial Application N rec as a function of NDVI 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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) 4/7/2019 NUE Meeting

Yield Prediction New upper bound representing real “potential” 4/7/2019 NUE Meeting

Yield Prediction Data from Regional Project 4/7/2019 NUE Meeting

Yield Prediction Yield goal or yield potential is not a very good predictor of nitrogen rate by itself (78 sites) 4/7/2019 NUE Meeting

Response Alone Response alone is also not necessarily a good predictor (same 78 sites) 4/7/2019 NUE Meeting

Response Alone If we calculate response with the 40 lb N/acre yield in the denominator (same 78 sites) 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

- = Easier to Read GNUP-YPN GNUP-YP0 NUE Fertilizer rec 4/7/2019 NUE Meeting

Nitrogen Use Efficiency How is nitrogen use efficiency determined? Arbitrarily? Based upon several site-years worth of data in Ohio 4/7/2019 NUE Meeting

Spatial Application N rec as a function of NDVI 4/7/2019 NUE Meeting

Imposed Assumptions Some yield-goal based algorithms have limits Maximum attainable yield Maximum N application rate Minimum N application rate 4/7/2019 NUE Meeting

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) 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

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 4/7/2019 NUE Meeting

Thanks!!! Questions? 4/7/2019 NUE Meeting