Is it N time yet?

Is it N time yet?

By: Jeff Caldwell 03/19/2012 @ 11:03am

The calendar may not say so yet, but for a lot of Corn Belt farmers, spring has sprung.

So, as fieldwork begins -- which it has in a lot of areas after days of 60- to 80-degree temperatures -- it's a good time to take stock of your nitrogen situation, specialists say.

First, did you put down nitrogen last fall? If so, you may have lost some -- if not all -- of it on account of the dry fall and winter, says University of Minnesota Extension nutrient management specialist Daniel Kaiser. If you have lost fall-applied N, your best bet's to sidedress later on this spring. But, before you put anything down, finding out if you're short will likely have to wait until the soil's warmed up a bit.

"Soil sampling for soil nitrate-N at this time is unreliable and will likely not give an accurate picture of what is still contained within the soil. The soils have started to warm," Kaiser says. "At this point in time (March 18), we would not expect a large amount of conversion of ammonium to nitrate within the soil if the fall applications were applied according to NBMPs, such as application when soil temperatures are less than 50 degrees and the anhydrous band was sealed and did not volatilize out of the soil after application."

Did you hold off on your N applications last fall? If you waited until this spring to put it down, the warm end to winter and projected beginning to spring may compel you to get started on the early side. If you are considering this, pay close attention to your soil types. If you apply nitrogen now in some soils, little to none of it may be left in the field when you go to plant.

"Soil conditions do appear to be ideal for application but there still is some risk associated with application this early in the season. First, if you have sandy soils you should not consider early application. Nitrogen applied as part of the starter and a side-dress application is the best practice on sandy soils," Kaiser says. "For heavy textured soils that have not had a fall N application, a grower should consider using a soil nitrate-N soil test for prediction of N application rate. Since we had a dry fall and winter, there is good chance that there is a significant amount of soil nitrate left in the soil that the corn crop could use."

If you do want to test your soil before you apply anything, Kaiser recommends testing to a depth of 2 feet. If you're farming heavier soils that can hold on to nitrogen better than lighter, sandier soils, you're likely not as short. Even if you do put down supplemental N in a situation like this, timing is important.

"The majority of the crop uptake tends to occur after the V5 growth stage or when the plant is about a foot tall. Having most of N in nitrate form when the plant is not actively growing does present some risk," Kaiser says. "While the weather is warm it is hard to tell what may occur a month of more later."

What about nitrogen inhibitors? Can they help stem loss if you want to apply it now but have concerns about losses later this spring? Some are effective, but their efficacy and its length hinge greatly on the soil moisture and temperature. "Two chemicals that have been shown to slow nitrification are Nitrapyrin, the active ingredient in N-serve and Instinct, or DCD. These are the only two inhibitors shown to consistently slow the conversion of ammonium to nitrate," Kaiser says. "If the temperatures are warm and the soil is dry, there is concern of urea volatilize before it can convert to ammonium. Agrotain is a product used to slow the activity of urease which converts urea to ammonia and the best use for this product is when urea is surface applied and not incorporated. Normally it takes an average of 0.25 inches of rainfall to effectively incorporate urea into the soil. Agrotain extends the amount of time for this to occur."

Agriculture.com Crop Talk members say they've used nitrogen stabilizer producers with a degree of success, while other products aren't as effective in bumping yields. Crop Talk advisor Pupdaddy says he's used nitrogen stabilizers and phosphorous enhancers both, and the former's typically performed better for him than the latter.

"if it makes you sleep better when you apply nitrogen before planting, then by all means add an inhibitor. The same with the phosphorous enhancer...I don't worry about it too much, because I apply some phosphorous as a pop-up in the row and hardly ever see deficiency from it," Pupdaddy says.