Split application of nitrogen (N) in corn has been shown to offer many benefits to farmers, including a reduction in the total N required to produce a high-yielding crop. In-season application matches N supply closer to corn’s uptake pattern, and because of this, there is less nitrogen sitting in the soil in forms available for loss for long periods of time.
In the midst of a hot, dry spell for much of Ontario as we move into side- and top-dress season, many growers are asking how these conditions affect the risk of N loss, and whether a nitrogen stabilizer makes sense for in-season N applications.
Urease inhibitors are likely to provide added value to in-season N applications in 2023.
However, the value that urease inhibitors, and nitrogen stabilizers in general will provide depends greatly on what, when, and where that N is applied, and soil conditions in the field. Read on for more information.
How nitrogen stabilizers work
Nitrogen stabilizers come in three major types:
Urease inhibitors slow down the conversion of urea to ammonium. In the presence of high pH in the soil, the ammonium can rapidly convert to ammonia gas, which can be lost to the atmosphere through volatilization. This is especially true if the urea is at the soil surface. Urease inhibitors keep more of the N in the urea form for longer, where it’s safer from loss, until a significant (more than 0.5” or 12mm) rain can move it into the soil.
| Product name | Used with | Active ingredient |
| Agrotain | UAN, urea | NBPT |
| Anvol | UAN, urea | Duromide + NBPT |
| Nitrolizer | UAN, urea | NBPT |
| SylLockUp | UAN, urea, liquid manure | NBPT |
Abbreviations: NBPT – N-{n-butyl]thiophosphoric triamide; UAN – liquid urea-ammonium nitrate
Nitrification inhibitors slow down the conversion of ammonium to nitrite and then nitrate. Nitrate is a plant-useable form of N, but is also highly mobile in the soil and can be lost in multiple ways, including:
- Leaching – downward movement of nitrate-N through the soil profile
- Dentrification – atmospheric loss of nitrate-N as nitrous oxide and nitrogen gas under anaerobic conditions (waterlogged soils)
Nitrification inhibitors keep more of the N in the ammonium form for longer, which is more stable once in the soil and still plant available.
| Product name | Used with | Active ingredient |
| Centuro | Anhydrous ammonia, UAN | Pronitridine |
| eNtrench NXTGEN | UAN, urea, liquid manure | Nitrapyrin |
| N-Serve | Anhydrous ammonia | Nitrapyrin |
| SylLockDown | Anhydrous ammonia, UAN, urea, liquid manure | DCD |
Abbreviations: DCD – Dicyandiamide; UAN – liquid urea-ammonium nitrate
Dual inhibitors combine urease and nitrification inhibitors to protect N in the soil from all major loss pathways. These are the most effective at reducing greenhouse gas emissions from nitrogen fertilizers as well.
| Product name | Used with | Active ingredient |
| Excelis Maxx | UAN, urea | DCD + NBPT + stimulant |
| Neon Surface | UAN, urea | DCD + NBPT |
| SuperU | Urea (pre-coated) | DCD + NBPT |
| SylLockPlus | UAN, urea, liquid manure | DCD + NBPT |
| Tribune | UAN | NBPT + Pronitridine |
Abbreviations: DCD – Dicyandiamide; NBPT – N-{n-butyl]thiophosphoric triamide; UAN – liquid urea-ammonium nitrate
The verdict is in: nitrogen stabilizers work. Agronomically and environmentally, they are effective in reducing risk of losses for every nitrogen application. It’s the economic part of the equation that may differ between growers, fields, application methods, and on a season-to-season basis. It’s worth looking at your operation this growing season to determine whether the benefits of loss reduction are worth the additional cost.
What is the risk of nitrogen loss in 2023?
Volatilization is most often the number one form of nitrogen loss from corn fields. How much N is lost depends on the weather and soil conditions. High soil moisture at application followed by warm, dry, breezy conditions is the worst case scenario for N loss from urea. These N losses come rapidly – research shows 16-25 kg N/ha (14-22 lb N/ac) per day for the first 3 days, and continued loss for long after until a significant rainfall comes.
In contrast, a soil with minimal moisture content at the time of application has very little volatilization loss initially. The conversion from urea to ammonium requires water for the enzymes; without soil water, the conversion slows and the N stays in the urea form. However, this conversion does still occur over time, and lack of a significant rainfall event can still lead to substantial N loss. Research shows losses can continue for at least 1 month following application with lack of significant rainfall, and total loss of over 31% of applied N in dry conditions.
Urease inhibitors protect against volatilization, and can reduce N loss from your application, depending on how you plan to apply in-season. From a loss perspective, research from Drury et al. (2017) has shown that with untreated urea in a broadcast scenario in-season, 31-68% of the applied nitrogen can be lost due to volatilization. With sidedress N rates of 117 lb N/ac (130 kg N/ha), 36-80 lb N/ac (40-88 kg N/ha) was lost in this study.
In comparison, injecting UAN with a dual inhibitor can eliminate volatilization losses, as well as reduce denitrification losses, and increase yield by 33 bu/ac.
When deciding between different types of nitrogen stabilizers, it’s important to know what loss pathways you are reducing. As mentioned above, nitrification inhibitors have value in moist or waterlogged soils, where there is more risk of denitrification and leaching. Often, nitrification inhibitors have a better fit with early applications and high rates of upfront N. Urease inhibitors offer the best protection in-season.
Evaluating your risk
Evaluating risk of N loss using the 4Rs and your own application setup can help you decide whether using a urease inhibitor is the right call.
The Right Source:
Are you side-dressing UAN or top-dressing urea? Urea as a N source is most at risk for ammonia loss. A little less than ½ of the N in UAN is in the urea form, so right off the bat, it’s less prone to loss than urea.
Other forms of nitrogen vary in loss potential from volatilization. Anhydrous ammonia can be subject to major losses unless it’s placed deep in the soil, and can cause crop injury in-season as well. Manure can vary drastically in ammonium content as well as pH, while ammonium nitrate is a relatively low risk, albeit expensive option for in-season N application.
| Higher risk of N volatilization loss | Lower risk of N volatilization loss |
| Urea | UAN |
| Anhydrous ammonia | Ammonium nitrate |
The Right Rate:
The more N you apply, the more N that is available to be lost. Higher concentrations of ammonium and/or nitrate in the soil through large applications are what drive loss pathways to speed up. Twenty-five percent loss of 50 lb N/ac is less than 25% loss of 100 lb N/ac, and so the payback to protect can be greater with higher rates.
| Higher risk of N volatilization loss | Lower risk of N volatilization loss |
| More than 50% of N in-season | Less than 50% of N in-season |
The Right Time:
Are you beginning your side-dress application right after the corn spikes through? Or leaving it until the applicator is bending corn getting through the field? Maybe you are using a high-clearance machine to get through waist-high corn with a late application?
The closer you can time your N application to just ahead of when the corn will utilize it, the less that will be available in a vulnerable form in the field. See Figure 1.
Larger corn has a thicker, more robust canopy that can aid in reducing risk of volatilization. Slower winds, and cooler temperatures can be found under the canopy of larger plants, which prevents ammonia from moving off site as quickly as it does with smaller plants.
Timing your application ahead of a good rain (greater than 0.5”), means there’s less time available for it sitting on or near the soil surface where the risk of volatilization is high.
| Higher risk of N volatilization loss | Lower risk of N volatilization loss |
| Application at 3-leaf stage | Application at 8-leaf stage |
| Ahead of 0.1” (2.5mm) rainfall, then dry | Ahead of 1” (25mm) rainfall |
| No significant rainfall for 2 weeks |
The Right Place:
Coarse-textured soils (e.g. sands) and soils with high pH are most prone to ammonia loss, although high rates of volatilization can occur on any soil given a driver for those losses.
Knifing the nitrogen at least 2” below the soil surface can prevent most volatilization, while nitrogen sitting on the soil surface is most at risk of loss. Ensure that your fertilizer band is properly closed, and not sitting open to the air.
Surface banded or Y-Drop style application involves dribbling UAN in a band next to the emerged corn rows. While this brings the N closer to the rooting zone, it still requires significant moisture to move N down to the roots and lower the risk of volatilization.
| Higher risk of N volatilization loss | Lower risk of N volatilization loss |
| Coarse-textured soil | Fine-textured soil |
| High pH soil | Neutral or low pH soil |
| Surface broadcast or banded | Injected at least 2” below surface |
Decision time: does a urease inhibitor benefit my operation?
Identifying your risk level based on your application style and current weather and soil conditions is the key to answering this question. If your application mirrors factors that are more on the “higher risk” side, urease inhibitors likely make agronomic and economic sense to utilize.
If your application favours factors on the “lower risk” side, judge for yourself whether the added protection is worth the additional cost of the N stabilizer.
With high priced nitrogen still a factor, it’s hard to justify applying an extra few pounds of “insurance N” if you feel you are at medium or high risk of N loss.
It’s important that the nitrogen stabilizer you use offers the loss protection that you are after as well. A nitrification inhibitor won’t help with volatilization loss in dry weather, so check with your Certified Crop Advisor to ensure that you are using the right stabilizer for your in-season N application.
Sources:
Drury, C., Yang, X., Reynolds, W. D., Calder, W., Oloya, T. O., & Woodley, A. L. (2017). Combining Urease and Nitrification Inhibitors with Incorporation Reduces Ammonia and Nitrous Oxide Emissions and Increases Corn Yields. Journal of Environmental Quality, 46(5), 939–949. https://doi.org/10.2134/jeq2017.03.0106
Munroe, J., editor. (2018). Soil Fertility Handbook, Publication 611. Ontario Ministry of Agriculture, Food, and Rural Affairs. https://www.ontario.ca/page/soil-fertility-handbook
2 thoughts on “Do I need a Nitrogen Stabilizer with In-season Nitrogen in Corn?”
Comments are closed.