Navigating Nitrogen Management in Wet Spring Conditions – Nitrogen Loss Mechanisms

May 28, 2024 8:26 PM
Blog Post

This is part one of a three-part series on nitrogen management this spring. Read part two, “Navigating Nitrogen Management in Wet Spring Conditions – Estimating Nitrogen Losses,” and part three, “Navigating Nitrogen Management in Wet Spring Conditions – Does the corn need more nitrogen?”.

Image of standing water in a corn field.

Once again, Iowa finds itself grappling with the challenges of a wet spring, prompting concerns about late planting, nitrogen (N) loss, and the necessity of supplemental N applications for corn. This recurring issue has become all too familiar, with a plethora of articles from my predecessor, John Sawyer, delving into the topic over the years. Amidst this backdrop, understanding the dynamics of N loss is essential. Factors such as tile drainage, especially prevalent in the spring, and soil saturation combined with warmth, exacerbate losses, primarily through leaching and denitrification. While some N loss is typical, its magnitude varies depending on several factors, complicating predictions regarding its impact on corn N supply and the need for additional fertilization. This series of articles will explore the intricacies of N loss mechanisms, delve into approaches for estimating N loss, and provide practical insights for effective nitrogen management in wet spring conditions.

Understanding Nitrogen Loss Mechanisms:

In the intricate process of nitrogen management, understanding the mechanisms of nitrogen loss is vital. Two primary pathways dominate: leaching and denitrification, each influenced by soil texture, drainage patterns, and climatic conditions.

Nitrate leaching, the process by which nitrate migrates below the root zone with soil drainage, is a critical mechanism contributing to nitrogen loss, especially in tile-drained landscapes common in Iowa. Nitrate, being a negatively charged ion, exhibits high mobility and readily follows the flow of water, particularly after heavy rainfall events. In areas with rapid drainage patterns, such as those found in tile-drained landscapes, the risk of nitrate leaching is particularly pronounced. This poses significant challenges for nitrogen management, as it can lead to reduced crop productivity, water pollution, and adverse environmental impacts.

Conversely, denitrification is a biochemical reaction, catalyzed by soil bacteria in oxygen-depleted, saturated conditions, that transforms nitrate into nitrogen gas. This process primarily occurs in fine-textured, poorly drained soils or areas prone to ponding, where the absence of oxygen prompts soil bacteria to metabolize nitrate to nitrogen gas that is released into the atmosphere. This process typically initiates after two to three days of soil saturation, with the rate of denitrification accelerating as soil temperatures exceed 55 degrees Fahrenheit.

Quantifying N Loss:

Quantifying nitrogen (N) losses through leaching and denitrification is like solving a puzzle with many pieces. To gauge the extent of potential N losses, it is essential to consider the conversion rate of applied fertilizer N to nitrate, the primary nitrogen form of concern for both leaching and denitrification. As soil temperatures rise above 50 degrees Fahrenheit this conversion process accelerates. Table 1 shows the approximate times for different fertilizers sources to convert to ammonium and nitrate. The conversion process of ammonium to nitrate can be delayed up to two weeks by using a nitrification inhibitor, while urea conversion to nitrate can be delayed up to 10 days by using urease inhibitors.

Table 1. Approximate time for different fertilizer sources to convert to ammonium and nitrate.

Fertilizer Source

Approximate time

until Ammonium

Approximate time

until Nitrate

AMS, 10-34-0, MAP, DAP

0 weeks

1 to 2 weeks

Anhydrous Ammonia

0 weeks

3 to 8 weeks

Urea

2 to 4 days

1.25 to 2.5 weeks

UAN

50% from urea in 2 to 4 days

25% is ammonium, 0 weeks

50% in 1.25 to 2.5 weeks

25 in 1 to 2 weeks

25% is nitrate, 0 weeks

Source: Dan Quinn, Purdue University. Adapted from other sources including Havlin et al., 1999

Estimating leaching losses of nitrogen can be difficult because factors such as soil drainage, crop N uptake, and N movement within the soil profile all affect the fate of leached N. Furthermore, it is important to note that even if N migrates downward in the soil profile, it may not leave the root zone remaining accessible to plant roots, thus reducing potential losses.

Denitrification losses depend on soil temperature and saturation duration. Higher soil temperatures can result in greater microbial activity which can expedite the conversion of nitrate to nitrogen gas, while longer periods of saturation extend the duration in which the microbes must metabolize nitrate for use as an oxygen source. Saturated soil becomes anaerobic within one to two days. Table 2 shows the approximate percent of soil nitrate lost per day via denitrification at different soil temperatures.

Table 2. Approximate percent nitrate-N lost per day via denitrification at different soil temperatures under saturated conditions.

Soil Temperature

Nitrate-N loss per day

°F

%

55 – 65

2 – 3

>65

4 -5

Adapted from Shaver et al., 2023 and Torbert et al., 1993

As we conclude part one of our series on nitrogen management in wet spring conditions, we've explored the intricate dynamics of nitrogen loss mechanisms, from leaching to denitrification. Understanding these processes lays the groundwork for part two of our series, where we will examine methods of quantifying nitrate-N formation and estimating potential losses, which are essential for making informed decisions in the face of unpredictable weather patterns and soil conditions.

This was part one of a three-part series on nitrogen management this spring. Read part two, “Navigating Nitrogen Management in Wet Spring Conditions – Estimating Nitrogen Losses,” and part three, “Navigating Nitrogen Management in Wet Spring Conditions – Does the corn need more nitrogen?”.

References:

Bechman, T.J., 2024. “Determine how much nitrogen is left.” Indiana Prairie Farmer, May 6, 2024. https://www.farmprogress.com/corn/determine-how-much-nitrogen-is-left

Sawyer, J., 2007. “Estimating nitrogen losses – early spring 2007.” Iowa State University Extension and Outreach Integrated Crop Management Encyclopedia, May, 14, 2007. https://crops.extension.iastate.edu/encyclopedia/estimating-nitrogen-los...

Sawyer, J., 2014. “Estimating Nitrogen Losses in Wet Corn Fields.” Iowa State University Extension and Outreach Integrated Crop Management Blog, June 17, 2014. https://crops.extension.iastate.edu/cropnews/2014/06/estimating-nitrogen...

Sawyer, J., 2016. “Precipitation and nitrogen this spring.” Iowa State University Extension and Outreach Integrated Crop Management Blog, June 6, 2016. https://crops.extension.iastate.edu/blog/john-sawyer/precipitation-and-n...

Sawyer, J., 2018. “Potential Nitrogen Loss- 2018.” Iowa State University Extension and Outreach Integrated Crop Management News, June 22, 2018. https://crops.extension.iastate.edu/cropnews/2018/06/potential-nitrogen-...

Shaver, T.M., Wortmann, C.S., Shapiro, C.A., Hergert, G.W., Anderson, B.E., Pavlista, A.D., 2023. Nutrient Management for Agronomic Crops in Nebraska. UNL Extension Publication EC155. https://extensionpubs.unl.edu/publication/9000016363764/nutrient-managem...

Torbert, H.A., Hoeft, R.G., Vanden Heuvel, R.M., Mulvaney, R.L. and Hollinger, S.E., 1993. Short‐term excess water impact on corn yield and nitrogen recovery. Journal of production agriculture6(3), pp.337-344.