Ontario Optimum Corn N-Rate Estimator Tool (“Delta Yield” Tool)

Posted on by Ben Rosser in Corn&Soil Fertility

The Ontario optimum corn N-rate estimator tool can be accessed by clicking the icon below.

(this is the same tool previously posted on gocorn.net)



Simple Summary

  • The Ontario optimum corn N-rate estimator tool (also known as the “delta yield” tool) provides an end-of-season estimate of the most economic rate of N based on yields from a low-N (<30 lb-N/ac) and high-N (N rate not limiting corn yields) strip
  • While this tool only provides an estimate of the optimum N rate, it offers a simplified approach for on-farm N assessments by avoiding the need for applying 5 N rates to develop a traditional N response curve.  



The Optimum N-Rate Estimator Tool

If you’ve wondered what the optimum corn nitrogen (N) rate is on your farm but don’t want to go to the trouble of applying 5 or 6 different N rates to develop a traditional N response curve, the Ontario corn optimum N-rate estimator tool (also known as the “delta yield” tool) may be for you.

This tool can estimate the optimum N rate after harvest with corn yields from just two N rates:

  • a low-N rate strip (ideally zero N, but no more than 30 lb-N/ac)
  • a high-N rate strip (a rate of N that is expected to not limit corn yields, typically standard grower rates + 50 lb-N/ac, but not less than 180 lb-N/ac)


The Delta Yield Concept

The low-N rate strip demonstrates the yield we can achieve with just natural soil N supply (say for example, 150 bu/ac in Fig. 1) while the high-N rate strip demonstrates the maximum yield we can achieve when N is not limiting (say for easy math, 250 bu/ac). The difference in yield (or “delta yield”) between these strips (100 bu/ac in this example) is the amount of yield we are trying to capture with fertilizer N. The smaller this difference, the lower the N response and the lower the optimum N rate. The greater the difference, the greater the N response and the greater the optimum N rate.

Figure 1. Screenshot of Ontario corn optimum N-rate estimator tool.


The Optimum N-Rate Estimator Tool

The optimum N-rate evaluator tool uses relationships observed between delta yield and the most economic rate of nitrogen (MERN) in the Ontario corn nitrogen database. These relationships allow us to estimate what the optimum N rate of a field might have been by calculating delta yield from only low-N and high-N rate strips. While this is only an estimate, Ontario research shows that these estimates can be very economically close to MERN calculated using a true response curve (Janovicek et al, 2020).


Using The Tool

This tool is a post-hoc test – it is using yields after the growing season to estimate what optimum N rates may have been for the area tested during that growing season. To use the tool, you enter:

  1. Your low-N strip information
    • rate of N applied
    • yield of low-N strip
  2. Your high-N strip information
    • rate of N applied
    • yield of high-N strip
  3. Your economics
    • expected corn price
    • expected cost of N

The tool is available in both imperial and metric versions.

Nitrogen rate information is used to determine if rates applied are within the limits expected to provide a confident estimate. It provides warnings where the amount of N applied in the low-N strip may have been too high (e.g. >30 lb-N/ac) or where the amount of N applied in the high-N strip may have been too low (e.g. <180 lb-N/ac).

Yield information is used to calculate delta yield to estimate the optimum N rate.

Economic information (N:corn price ratio specifically) is used to adjust the optimum N rate estimate for economics. As N becomes more expensive relative to corn, optimum N rates are adjusted downwards.


Output

The tool provides an estimate of what the optimum N rate may have been for the area tested during that growing season. It provides two outputs:

  • an optimal N rate above the low-N rate used (145 lb-N/ac in Figure 1)
  • a total optimal N rate that includes the low-N rate used (175 lb-N/ac in Figure 1, sum of 30 lb-N/ac of starter and 145 lb-N/ac optimum N rate).


References

Janovicek K, Banger K, Sulik J, Nasielski J, Deen B. Delta yield based optimal nitrogen rate estimates for corn are often economically sound. Agronomy Journal. 2021;113:1−13. https://doi.org/10.1002/agj2.20521