WHERE'S MY NITROGEN? HOW TO MAKE A NITROGEN MAP.

Many growers apply nitrogen in the fall to take advantage of the wide application window. But there are risks with fall application. Applying seven months prior to planting leaves nitrogen vulnerable to loss from rain events and warm winters.

Because nitrates easily move in the soil profile, it is important to map that movement to get a picture of your nitrate availability.

Pulling soil samples before planting, after emergence and prior to the rapid uptake period — v10 — gives you a timeline of N availability. In season sampling is different than the full-spectrum sampling done semi-annually. This is a specific sampling technique designed to find the ammonium and nitrates in the soil profile. Use row profile sampling, taking 10 cores every 3 inches across a 30 inch row to give an average of what that profile contains. This process allows you to find the bands of N from the injector knife or coulter and to see how this band is dispersing through the soil profile.

When you apply NH3, it’s important that your analysis look at nitrate — N03 — and ammonium — NH4 — levels. Ammonium is relatively stable, but converts to nitrate. Nitrate is mobile. Knowing how much of these two forms of nitrogen are in your field will tell you the amount of total N that could be available to the plant and how much of the total N is at risk of movement and loss. As the crop gets closer to silking, N03 levels are all that are necessary since most of your ammonium will be converted to nitrate.

Manage the root zone. Pull one-foot and two-foot cores in each of your management zones. The one-foot sample shows what’s available in the root zone. The two-foot samples show if the nitrogen has moved deep into the profile.

Here is an example. This field had 200 pounds of anhydrous ammonia applied in the fall. Samples were pulled prior to planting in two management zones.BY 360 YIELD CENTER.