Timing Spring Anhydrous Applications with Planting Time for a Successful Growing Season
Updated: Mar 28, 2019
We’ve been getting a lot of questions about the best practice options for what is shaping up to be a tight spring. We are unfortunately back loading a lot of field work with anhydrous left to apply, dry fertilizer needing to be spread, spring burndown still a priority, and some normal fieldwork to smooth up ruts and gullies after a wet harvest. We want to get all of these to get done before planting, but how do we make this happen? One of the most critical of these field trips is applying anhydrous. This can also be one of the most damaging if done incorrectly; apply too late or too close to the seed and plant burning and stunting will affect the plant all year long. This blog will cover the best options to get your nitrogen on, and still preserve plant health and yield.
What Happens When We Apply Anhydrous
When we put anhydrous in the soil, the NH3 molecules are rapidly changed to NH4+ molecules. This generally occurs when the NH3 split water molecules to gain the extra H+ ion. However, as this happens, OH- molecules are formed from the remaining molecules and this will raise the pH of the strip, and consequently slows down conversion from NH3 to NH4+. Because of this, some NH3 will remain in the soil, posing a risk to plants. Soils that have adequate soil moisture will do a better job of converting to NH4. As this reaction happens, the anhydrous will expand to about a 6 inch diameter cylinder. This zone will be larger in dry soils as the NH3 seeks moisture from farther away from the zone of injection.
The main risk to plants is when plant seedlings come in contact with some NH3 ions that have not converted to NH4+. NH3 is toxic to plants and will result in burning of roots, stunting of plants, and possibly even death of seedlings. If the plant lives through the damage, the root system will be stunted and result in more issues with plant standability, nutrient and water absorption, and ultimately will end with a reduction in yield.
With late applications of anhydrous, there is less time for the NH3 to make the conversion to NH4+. Normally when we complete this application in fall or in the late winter months, we give adequate amount of time for all the conversions to happen and the risk of anhydrous burn is dramatically reduced. Because our anhydrous-planting window will be much closer together, the risk for burn will be increased. However, there are several practices that can ensure anhydrous burn is eliminated or severely reduced.
Separate the Seed
The first, and most important practice is to separate the seed from the band of application. This can be through both time or distance.
There is no magic length of time between application and planting that will ensure you won’t have seedling damage. This is too dependent on temperature of the soils, moisture conditions at application and following, and soil texture. Generally, recommendations suggest planting at least 5-7 days after application. Some sources even suggest 14 days. However, be aware that this is very dependent on conditions. In the right conditions, you could plant the next day. If conditions are bad, it could be months after application and still cause damage.
Distance is really more of a priority than time. A study from Illinois showed that at a 200 lb per acre rate, there was no stunting when anhydrous was injected at 10 inches deep and corn was planted the same day. Severe and slight stunting were visible at this rate at 4 and 7 inch injection depths respectively. Stand was reduced when 200 lbs was applied at 4 inches, but there was no stand reduction when injected at 7 and 10 inches. At a lower rate of 100 lbs, the study showed no reduction of stands at any of the depths, but some stunting at 4 and 7 inch depths, and no stunting at 10 inches. The study concluded that “Overall depth of NH3 injection was more important in reducing injury than was the amount of time between NH3 application and planting.” Set your applicator as close to 10 inches as you can go. Unfortunately, this will not be possible with high speed applicators. You will not be able to set the applicator deep enough to minimize damage. Use an alternative method for reducing risk, or use a different applicator.
Another option to increase distance between the application and planting is to offset rows. Keep track of where you anhydroused and then plant between those locations by using GPS. This will keep the distance from plants at least 15 inches away from the row. This application can also be done every other row at a double rate with no negative consequences. If you don’t have GPS and can no longer see your rows, anhydrous at an angle to where you want to plant. This will ensure that you don’t have rows running completely on tops of anhydrous and result in damage to the whole row.
As shown in the study from Illinois, reducing rates can help reduce the risk of anhydrous burn. Lower rates are more likely to be converted into NH4+ and not detrimentally affect the plant. While you may worry that lower levels are not enough to supply the plant, remember that the majority of N uptake occurs after V8. Applying a lower late and then planning on an additional sidedress application will often provide a more environmentally friendly, and economical fertilizer application.
If you do apply a lower rate up front, make a plan for what your summer sidedress application will be. Will you go in with an anhydrous rig and side dress later? Will you wait until the plants are too tall for that and come in with a high clearance applicator? Are you planning to have nitrogen flown on by plane? Make a plan for your source for sidedress and get it set up early.
Services like Encirca or crop canopy sensors can help you determine what your in season nitrogen need will be. Encirca will take into account how much and when you applied and calculate what amount of nitrogen your crop will need. Talk to one of the team to learn more.
Sources of Fertilizer
Some people might have the tendency to switch to a different fertilizer source as we get closer to planting. There is really no need to switch sources as long as you can get the anhydrous a safe distance from the crop. Additionally, switching sources may not be feasible when equipped to run anhydrous. Keep in mind when switching to a dry or broadcast application that a rain will be needed shortly after to prevent loss from volatilization.
Applying anhydrous close to planting time is an option. Just follow a few precautions.
1. Distance is more important than time. Keep the seed and injection band as far from each other as possible. Injection depth should be greater than 7 inches, and preferably closer to 10 inches.
2. Split the anhydrous rows when planting. This will keep the seed away from the injection zone. If you can't split rows, plant at an angle to the rows to ensure an entire row won’t have problems with stunting or stand reduction.
3. Consider a split application. Lower rates will reduce risk of damage. Split applications will also result in less nitrogen loss throughout the season, allow us to tailor specific rates based on crop need through Encirca or crop canopy sensors, and will often be more economical.
4. Unless you CANNOT get into the field before planting, there is likely no reason to switch fertilizer sources. Use the previous precautions, and your application should go smoothly.