Nitrogen moves in the soil profile because of environmental factors – precipitation, temperature, etc. – but it’s important to understand the chemical process happening behind that movement in order to better control it.
Let’s start by reviewing the transformation of one form, Anhydrous Ammonia. It enters the soil ammonia (NH3). It quickly grabs a hydrogen molecule and becomes ammonium (NH4). Next, the relatively stable NH4 coverts to nitrite (NO2) and with the addition of oxygen molecules, to nitrate (NO3-) which is the form plants put to use. This process of NH4 -> N02 -> N03 is nitrification.
Anhydrous depends on the moisture in the soil move it to the more stable ammonium form. NH3 grabs on to the H molecule from water (H20) and quickly converts to ammonium. If there isn’t moisture available in the soil, the NH3 would volatilize and be lost into the atmosphere, This occasionally does happen in some fall applications when higher rates are being applied into dry soils or if the furrow isn’t closed properly.
Ammonium is positively charged, so it remains stable in the negatively charged soil. This is where CEC or cation exchange capacity comes from – the ability to hold positively charged ions called cations. PH can plays a role in ammonium stability. If you have an extremely high pH or Alkaline soil you may be susceptible to increased volatilization. This is kind of a catch 22 though because ammonium based fertilizers are a good way to lower soil pH.
Nitrification is process that converts ammonium to nitrate. We often think of nitrification as a bad thing, but it is a double edged sword: nitrification is needed to make the nutrient available to the plant but it is also the reason nitrogen is mobile and moves out of the root zone. Nitrogen loss occurs because nitrates are negatively charged, like the soil, causing the nitrates to be mobile and move with moisture deeper into the soil profile.
So why does this process matter? Well, when you’re applying NH3 in the fall, you’re putting out the crop’s source of nitrogen seven months before it will use it. After the ammonium endures the cold, then warm, dry then wet winter, much of the ammonium has converted to nitrate – and is susceptible to movement and loss.
Here are a few tips to help you overcome nitrogen loss and use this process to your advantage:
- Use nitrification inhibitors when applying NH3 months ahead of planting. This will prevent the conversion of NH4
- Use anhydrous as a nitrogen base, providing the plant’s need during the early stages of growth. Then resupply nitrogen based on environmental conditions and current nitrate levels. Rember that a corn plant takes up 75% of its nitrogen after V10. Saving back some nitrogen for later in the season can help you adjust accordingly.
- Soil test in the spring and throughout the growing season. This could mean using in field soil testing technology or sending it off to a lab. Going into the growing season with a better understanding of where your nitrogen is and continuing to manage those levels instead of guessing will help you to better serve your crop.
- Consider utilizing mid-or-late season application technology like 360 Y-DROP. This system allows you to measure, wait and let mother nature run her course, and then come back and apply with the rate that the crop needs.