Warm, Wet Conditions Affect Pre-Plant N Application

While we all enjoy the warm fall weather, these warm temperatures in conjunction with a delayed soybean harvest create some issues for growers intending to apply fall anhydrous.

Most growers understand the importance of waiting until soil temperatures have dropped below 50 degrees in order to dramatically slow the conversion of ammonium nitrogen to the nitrate form. But these warm, sunny days in combination with a delayed soybean harvest dictate a much tighter window to apply the anhydrous this fall. If the turn in temperatures coincides with the wet weather, many growers will be forced to make difficult decisions. Applying when the soil is too wet can create smeared slots that allow the gas to migrate towards the surface. Soils will warm much more quickly near the surface next spring, which could lead to a quicker conversion to the nitrate molecule. In this case making a total application of next year’s nitrogen is a risky proposition.

But growers do have options:

  1. Stabilize fall N with a nitrification inhibitor and apply at slightly warmer soil temperatures while the soil is still fit. Depending on soil temperatures and pH, nitrification inhibitors can delay conversion anywhere from 4-10 weeks. Keep in mind that soil type, climate and cultural practices can have a large impact on this process. This option is acceptable however it also carries some risks of exposure next spring depending on soil and weather conditions.
  2. Delay application of anhydrous to a pre-plant spring application. This also carries inherent risks regarding not only the window of application, but a squeeze on time and manpower resources at a critical time of the year.
  3. Apply a stabilized base rate this fall and apply the remainder of your nitrogen in-season which could include adding to your base rate at planting. Then take measure of the year at hand and measure in-season needs before finalizing your final N application. By applying a base rate and waiting until the crop is actively growing, it provides the ability to judge whether excess loss dictates additional N to supplement the crop or additional mineralization of organic N allows for a reduction in the final application thus saving on input costs without sacrificing yield.