Last week, I wrote about the function of N in plants. While I can easily spiral into a biochem nerd-out when I talk about N, I hope that you were able to pick up on one essential message from that article: N is really freaking important to your plants.
The last thing we want to do is lose it, and the unfortunate thing about this all is that for however important N is, there are a lot of ways to lose it. When the only thing we want it to do is go in (our plants), it often ends up going up (in the air), down (in the ground), or just gets plain old stuck (in minerals).
I’m going to throw some biochemistry at you here, but I’m going to keep it simple and purposeful. Knowing what happens to your N once you apply it and why it happens will help you to make some more informed, thus better, decisions about managing your most essential nutrient.
Let’s start with the good. Three possible good things can happen when you put N on your field:
- Your plant uses it. No explanation necessary here—this is the ultimate goal.
- It becomes fixated. This occurs when N2 gas is converted into NH4, which is ammonium. Ammonium is totally useful to your plants, so fixation is basically a step toward your ultimate goal.
- It becomes mineralized. Mineralization occurs when organisms release N from soil organic matter such as NH4. Like fixation, mineralization is a step in the right direction, so it’s something to feel good about.
Now for the neutral. Two things might happen to your N before it is used by your plants, neither of which is necessarily good or bad. These things simply just are.
- N is hydrolyzed. Hydrolisis is the conversion of urea to NH4. As you know, NH4 is useable to your plants. Hydrolysis is simply a necessary step that reduces carbon-rich N to a form that is available for plant uptake.
- N becomes immobilized. As the name suggest, immobilization occurs when N gets atomically tied up with residue. To remobilize it for use by the plant, you need a few microbes to make a lunch of it. They free it up for use through the process of mineralization.
And now the ugly. There are more than three ugly pathways for N, but these are the three main avenues. All of these lead N out and away from your plants. I’ll hit you with some practical solutions to these in addition to the chemistry because it’s how to stop these things that matters most:
- Volatilization causes N to be lost to the air. In volatilization, conditions including warm soil temperatures, oscillation of soil moisture levels, and an open canopy cause the loss of NH3, a gas, from NH4. That good NH3 then floats into the air, leaving just a lonely H in the soil. Fortunately, volatilization only affects surface applied N, so quick incorporation of N provides an effective solution to volatilization.
- Denitrification also causes N to be lost to the air. As with volatilization, conditions cause NO3 to separate, this time into N2, also a gas, which also floats away in the air. Conditions that cause denitrification are slightly different than conditions that cause volatilization: denitrification occurs in fully saturated soils with warmer temps speeding the reaction. Because soil must be fully saturated, denitrification is a localized problem, but is nonetheless responsible for our greatest short term losses of N. Denitrification is solved by avoiding compaction and increasing your soil’s infiltration rate.
- Leaching causes N to sink too deep in the soil to be used by your plants. Through the process of nitrification (which I won’t bother you with here), NH4 is converted into NO3, which is also useable by plants, but which is water soluble and thus subject to leaching. Time is the main requirement for turning NH4 into NO3, and water is the vehicle that takes NO3 out of range. Therfore, leaching is avoided by well-timed applications of N. It is best applied close to the time when plants actually use it, and outside of the rainiest parts of our year. This means avoiding applications during May through mid-June which is by far the worst stretch for leaching: N applications made during this date range put N in the soil too early for plant use and during our months of heaviest precipitation.
You might notice that the preservation of NH4 is highly desirable. The good things here make NH4. The bad things break it. Our goal is to stop the things that break it, and we’ve got two main weapons with which to protect it: time and chemistry.
Corn uses 2/3 of the N it requires in a window that is less than 5 weeks long. Making our N applications right before this window reduces the time that our valuable N is just sitting in the field, waiting for bad things to happen to it. Good timing preserves NH4.
The other weapon, chemistry, is the more science-y route, but is totally effective. I’m talking about N stabilizers here, which work on an anatomic level to form a barrier around your NH4 to protect it from the whims of temperature and water that seek to change it and take it away.
Regardless of the source of N you use, one or both of these weapons can be used to protect your precious investment. If you’re uncertain about the best bet for your particular situation, your Central Valley Ag Field Sales Agronomist is more than happy to speak with you and assist you in making the best decisions for your operation.