Improve Fall Nitrogen Practices

In most of the US, this fall was a wet one. Chances are, you didn’t get much of a chance to get fall anhydrous in the ground.

You may have missed the window this year, but here are some tips to keep in mind for next year.

1. At what rate/ threshold of N application do results plateau? 

When developing a nutrient management plan a good place to start is with the 4Rs system: the Right rate, the Right source, the Right placement, and the Right timing. The 4Rs are interrelated and have to be adjusted based on some decisions that you as a grower need to make, but the first step is to decide on what is the right nitrogen rate. This is not an easy answer. Common factors that affect suggested N rates are timing of application, climate, crop rotation, tillage system and soil productivity. When using too little N, a crop such as corn results in lower yields and reduced profits. However, if too much N is applied, profits will be reduced, and environmental impact is likely to occur. Applying most the crop’s N requirements closer to when the plant will use it will result in more efficient uptake and will likely reduce the overall total pounds of N needed. Many land-grant universities have either a Nitrogen calculator that can be used or equations that will help you get started. For a Regional (Corn Belt) Approach, the Maximum Return To Nitrogen (MRTN) can be calculated using a web-based tool called the Corn Nitrogen Rate Calculator. The calculator can be found here. The MRTN, profitable N rate range, net return, % of maximum yield, and other information can be calculated directly from N response trial databases for each state. If you still have questions contact your local agronomist, extension agent or soil extension specialist for you state.

2. What are recommended application depths of anhydrous ammonia depending on conditions?

When applying anhydrous ammonia (AA) a depth of at least 6-8” should be maintained. In dry soils, a deeper depth may be needed to get in some moist soil.

3. What problems could various conditions bring to application/nutrient availability?

Ammonia applied in coarse, dry or cloddy soils tend to move from the injection site where considerable amount of ammonia may be lost within just a few days if soil is not sealed well or the injection depth is too shallow. However, ammonia applied in wet soils may move up the injection track if sidewalls are smeared by the anhydrous applicator. Wing sealers (beaver tails) are available that help close the ammonia track. If you smell ammonia after a pass from the anhydrous applicator, adjust your equipment or consider waiting for soil conditions to improve.

4. What are ideal conditions for anhydrous ammonia application? 

When anhydrous ammonia is applied it quickly reacts with organic matter, clay particles, free hydrogen ions, and, most importantly, with soil, water, preventing volatilization of ammonia. Anhydrous ammonia losses to the atmosphere at the time of application depend mostly on soil moisture and depth of injection. Ideal soil conditions are around 15% to 20% soil moisture. An adequate application depth under ideal moisture conditions is about 6’’ for fine-textured soil and 8’’ for coarser textured (sandy) soil.

5. How does spring application practices/ recommendations vary in corn-on-corn? 

The length of the time between applying anhydrous ammonia and when you can plant depends on several factors: AA rate, soil moisture, and application depth. The only risk of planting soon after application is if seeds fall within the ammonia retention zone. To avoid seedling injury, an increase in time or space can be important. If application conditions are less than ideal, then 3 to 5 days before planting is typically enough of a wait to reduce the risk of seedling injury. Under ideal soil moisture conditions and proper application depth of a normal application rate (100 to 200 lbs. N/acre), there is typically little risk of seedling injury, even if seeds are planted on top of the application zone right after AA application. That said, I would still not recommend intentionally planting on top of the AA row. If you have RTK guidance, it is very easy to apply AA between the future corn rows. If RTK guidance is not an option, I recommend applying AA at an angle to the direction of planting to minimize the potential for planting on top of the AA band.

6. When would you recommend post-plant N applications? Can a farmer gain value from it?

The goal of timing nitrogen (N) applications to corn is to supply adequate N when the crop needs it, without supplying excess that can potentially be lost. Applying N at multiple times can spread the risk of N loss and crop deficiency. Corn requires only a fraction of the total N it needs during the seedling stage, but its needs increase rapidly once corn reaches the V8 growth stage (8 leaf collar stage). Corn from V8 to tassel/silking stage (VT/R1) can be reached in about four weeks if conditions are favorable. During this period over half of its total N supply is needed and still the corn plant needs about one-third of plant N during the reproductive (ear-fill) period.

Quite often wet weather can interrupt your spring plans prior to planting. If you get behind with fertilizing prior to planting a post-plant nitrogen application on corn is still an option. Some suggestions include, in order of preference:

• Side-dress inject AA or UAN solutions. Injection can be effective between every row or between every other row.
• Surface dribble UAN between corn rows or between alternating rows.
• Broadcast dry granular urea, UAN solutions, ammonia nitrate or ammonium sulfate.

* Some type of row cultivation is best after surface application of urea and UAN to minimize volatile loss.

In-season (sidedress) N applications allow a grower to adjust planned N supply based on weather variations. If in-season N application is well managed, a grower can glean its potential reward with increased yield.

7. Are there any additional insights on N application you have to add?”

SAFETY:  It is essential that anyone handling anhydrous ammonia wear the appropriate personal protective equipment (PPE), be equipped with the necessary response supplies and know how to respond in an emergency. For additional safety and health information pertaining to anhydrous ammonia click here.

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