Considerations on rescue nitrogen
Jul 15Considerations on rescue nitrogen
High clearance equipment has expanded the possibilities for applying nitrogen right up to tassel time, especially in fields or parts of fields where N deficiencies are apparent.
Here are a few considerations:
- Is it too late? The answer is generally no if the corn is pre-VT stage. Recent research out of the Corn Belt has confirmed that 30-40% of the total N uptake in a corn plant occurs after VT (tassel stage). So if the need is there, and you suspect soil N supply is limited, then there is still time to make additions.
- Should I use protected nitrogen? The protection you are looking for is protection from volatilization from surface applied N (either granular urea or UAN). This is what Agrotain® Ultra provides. Do not use protected N that slows the conversion process to nitrate (i.e. Agrotain® Plus or ESN) at this stage in the season as you want the N available as quickly as possible. The value of volatilization protection goes up significantly if you are applying the N on soils that are damp on the surface but where rain is not in the forecast.
- Can soil nitrate testing give me any guidance as to how much N is required? Soil nitrate tests in advanced corn are generally very difficult to interpret. Plant nitrate uptake makes it difficult to use the soil nitrate test as any sort of rate determination. Low values (less than 10 ppm) support the need for more N, higher values (over 20 ppm) probably indicates that more N is not warranted. You cannot hope for more accurate results than that in July.
- How much N should be applied? If the total N applications have been modest up to near tassel or you are concerned that N has been lost from denitrification or leaching, then 50-75 lbs N/acre is probably a reasonable target.
- Can yield be recovered from wet holes? In situations where water has sat for extended periods and the corn has been severely compromised (completely yellow), there may be little yield increase by applying rescue nitrogen. However, if the corn looks reasonably sound and has more classic N deficiency symptoms (yellowing down the middle of the leaf), then significant yield recovery from pre-tassel N is possible.
- Can foliar applied N do the job? This is an ongoing research question. Clearly, the total amount of N that can be applied via a foliar application is very limited (i.e. foliar forms of N generally provide 2-3 lbs of N per gallon of product) and application recommendations call for something in the range of approximately 2 gallons per acre in solution. So the total N applied might equal 5 lbs per acre. The question then becomes can this 5 lbs stimulate plant activity, help it recover from N deficiency and get the plant to take up additional N from the soil? Answers still to come on that one, but it might be an interesting strip trial to run on one of your fields that looks short on N. Remember to leave some check strips!
Maizex Seeds Agronomy Lead