Go away. For now. You’re causing anxiety.
We’ve gotten a lot of rain lately. A lot. And on cue, the questions have started: What about nitrogen loss?
Well, what about it? It’s a good question. One of the right questions. But the answer, of course, isn’t as short. Today, I can make a strong case not to be alarmed yet, but conditions have been interesting enough lately that one field may be fine while another is not. So an investigation is in order before you make any decisions to apply additional N, or not.
In my mind, our light is flashing yellow. Caution. So while I don’t believe that we’re in dangerous territory yet, I don’t want any of you to feel a false sense of security. Somewhere in between useless anxiety and false security is a place of heightened sensitivity. That’s where we need to be. Because parts and components of the situations that make for nitrogen loss are present, but it isn’t a perfect storm.
Current conditions might allow for loss through leaching and denitrification. A third pathway of loss, volatilization, is a nonfactor for now.
Leaching is the more widespread concern because the conditions that allow it to happen are fairly simple to meet: gravitational water and available nitrate. Gravitational water is, simply, a soaking rain. A grower mused to me recently that we lose our minds over a five-inch rain but generally chirp along pretty happily with a three-inch rain, though both can cause nitrogen loss. And he’s totally right. The five-inch rain is generally more destructive—soil often moves with a five-inch rain—but a gentler three-inch soaker still provides a lot of water moving downward through the soil. If there is nitrate there to be lost, a three-incher can help it along just as effectively as a five-incher.
So we meet the condition of gravitational water. In spades. The reason that I’m not in crisis mode over the potential for leaching is that there might not be a ton of nitrate available to lose. Nitrate is formed from ammonium, which is formed from urea, which means that a source of nitrogen must go through a process before it is lose-able via leaching and that process requires warm soil, which has not been a consistent condition around our territories. Soil temperatures have been on a roller coaster ride so far this season, which means that whether or not you have a lot of nitrate in your soil is variable.
Denitrification is a concern localized to ponded or absolutely saturated soils. In denitrification, anaerobic organisms convert nitrate to nitrite and then to nitrogen gas. Now, there are plenty of occurrences of ponded and saturated soils around the area, but the second condition necessary for significant N loss via denitrification—soil temperatures around 70 degrees—is largely absent given the early date and generally cooler air temperatures.
Whether or not N loss is happening in your fields depends on if conditions are met and to what extent. I doubt that N loss is widespread at the given moment, but that doesn’t mean that its not happening in your field. To know that, you need to monitor, and you need to measure.
The decision not to apply more N is just as important as the decision to apply more N and requires just as careful measurement and consideration. Soil samples are your friends. Tissue samples are your friends. Models are your friends (the mathematical kinds, at least). Don’t assume that because some conditions are met in some places that you need to apply more; and don’t assume that because all conditions aren’t met everywhere that you don’t need to apply. Quite likely, the answer is in the middle of these extremes: some places in some fields might need more N. Being open to this zone approach will allow you to be most efficient and precise with nitrogen and to best honor the four Rs as you proceed with operations this season.