1. Variable Rate Nitrogen Application in Corn Production
Jimmy Stotts
Precision Ag 4213

2. Introduction
Effective Management of fertilizer nitrogen (N) in corn production is needed to maximize economic return for producers and control N losses that can cause environmental problems. These environmental concerns with N use in corn are mainly focused on nitrate leaching to groundwater and surface water nitrate contributions to Gulf of Mexico Hypoxia.

3. Reasons for Variable Rate Applications
More economic return
Less environmental risk
Less fertilizer applied
Different soil types
No Grid Soil Sampling

4. Environmental cures Less amount of nitrogen leaching
Not near as much environmental risk with these variable rate applicators

5. Application Systems GreenSeeker
Great for late applications of fertilizer
These are Greenseeker sensors located on a Hagle High-Clearance Sprayer

6. Application Systems RT 500
Greenseeker Sensors on an Apache Spraying machine
2ftx2ft Resolution
Good for early fertilization

7. Other Application Systems
Soil doctor
Standard Ag Coulters
Paired “Rolling Electrodes”
“Plug Into The Soil”
One is positive and the other is negative
Conductivity
Electrochemistry
Complex resistivity

8. Challenges For VRT in Corn
The Potential Cost Savings Can be minimal
When all costs of developing and executing the variable rate strategy are considered the net return may be insufficient to cover the added expense.

9. Challenges For VRT in Corn
Prescriptive Nitrogen Strategies Involve Risk
These could include unusually favorable growing conditions or yield limiting events such as frost, hail, stalk lodging, pests, drought, or N losses due to excessive rainfall and denitrification

10. Check Strips (NRICH)
Needs to be several uniform check strips throughout the fields
A uniform rate should be applied based on current local or university recommendations
Additional strips with 50lb/ac above and below the recommendation rate may be helpful also
Can be harvested as separate loads on yield monitors or as a side by side comparison with a weigh wagon

11. Nitrogen Cycle

12. Application
If rates of applied N can be matched to actual corn N requirements throughout production fields, the economic and environmental goals of N management could potentially be achieved to a greater extent than would be possible with a single N rate applied to the entire field

13. Growth Chart

14. Application time (V5) Tassel formation
(V6) Yield can be closely predicted
(V9) Ear shoots develop
(V12) By waiting until (V12) it would be better for predicting potential grain yield

15. Adoption Of Technology
Variable Rate methods involving assessment of plant N status Through remote sensing during the growing season may have potential if the cost of these technologies does not exceed the value of the benefits provided

16. RETURN
Doerge(2001) estimated that the Nitrogen cost savings is in the range of 5-15$/ac
That is big time on 1000 acre farm

17. Sources http://www.neuse.ncsu.edu/nitrogen/