Question from a Subscriber of Crop Chatter: I’m setting up a triple shoot air drill with wide (12.6 inch) spaced seed shanks. Each seed shank has a 3.5 inch paired row seed opener with a granular fertilizer placement tube to put granular fertilizer in the center of each paired row. Additionally, the drill has mid row banding shanks on 25.2″ spacing to apply NH3. I have a 3 compartment air tank.
For cereals, I will place the seed and phosphorus together through the paired row openers, with starter urea placed in the middle of each seed row through the granular fertilizer tubes. For canola, the seed and phosphorus will be placed together with ammonium sulphate (and possibly some urea if a fertilizer blend is used) in the center of each seed row. For soybeans, the seed and granular innoculant will be placed together and phosphorus will be placed in the seed row centers. NH3 will be applied for cereals and canola through the mid row shanks with 1″ openers. The NH3 will therefore be up to about 7″ away from the furthest placed seed.
I’m trying to determine how to best split the total nitrogen rate between urea and NH3. Since NH3 is cheaper and less handling than urea, my preference is to maximize NH3 use. Given that I have heavy clay soil:
1) How long it will take the furthest away plants to be able to access the NH3?
2) How much urea should be applied to keep the crop well suppied with nitrogen until all plants can access the NH3 band?
Answer (provided by John Heard, MAFRI Soil Nutrition Specialist)
Crop roots access nitrogen in mid-row bands in 2 ways: roots growing laterally can intercept the band and mid-row placed ammonia converts to nitrate-N which then migrates as roots consume soil moisture. Usually mid-row banded nitrogen is available for crop growth by the time it is needed. Your seed-placed phosphorus fertilizer usually contains nitrogen to keep the seedling nourished. But we hear on occasion that early season crop yellowing (MN deficiency?) is observed in the situations here – cool, heavy clay soil with wide spaced mid-row bands. In years with warm, moist or dry soils, root access to bands will likely be quicker than this year. Fortunately you have an option to place some urea in a band close to, but safely away from the seed. I should think no more than 10-20% of the nitrogen requirement needs to be supplied there.