It's a question that arrives in our inboxes every spring without fail: "It's been raining — have I lost nitrogen, and do I need to apply more?" This year is no exception. With a highly variable spring precipitation pattern across Iowa (see map below) and corn now approaching or past the critical V6 growth stage, many producers are seeing yellowing in their fields and wondering what to do next.
Understanding Nitrogen Loss
Not all wet weather leads to meaningful nitrogen loss, and not all yellow corn signals an N deficiency. Before reaching for the fertilizer applicator, it's worth understanding the processes at work.
The two primary loss mechanisms are denitrification (the conversion of nitrate to gas under saturated, warm soil conditions) and leaching (the downward movement of nitrate with water through the soil profile). Both require nitrate-N to be present — ammonium-N and urea are generally not at risk until they convert to nitrate. The timing, temperature, and duration of saturation all influence how much loss actually occurs.
For a thorough breakdown of these processes and what conditions accelerate them, see: Navigating Nitrogen Management in Wet Spring Conditions – Nitrogen Loss Mechanisms.
Once you understand the mechanisms, the next question is how much nitrogen may have been lost. Several estimation approaches exist, from simple rules of thumb to more detailed calculations based on soil temperature and duration of saturation. These are covered in detail in: Navigating Nitrogen Management in Wet Spring Conditions – Estimating Nitrogen Losses.
Source : iastate.edu