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  • Writer's pictureRachel

5 Considerations for Fall Anhydrous

While we’ve seen a drop in soil temps at 2 inches and 4 inches during the last week, as this cold front moves out and we return to highs in the mid 50’s, we will be looking at some ideal soil temperatures for applying fall anhydrous. In the spirit of the busyness of this time of year, we are going to keep things short and sweet with the top 5 things to consider for fall anhydrous applications.

1. Temperature. While soil temps are less of a concern now with averages hovering in the low 40’s, earlier in the season can be a concern. Its imperative that we apply once soil temps are below 50 degrees to minimize the amount of nitrogen we lose to nitrification. If we apply at 50 degrees, the amount of nitrification is about a quarter of its maximum, and if we wait until 40 degrees, the amount of nitrification is nearly zero. At these temperatures we can reliably apply nitrogen and have it safe in cold storage for the duration of the winter. No one wants a 50% efficiency rate. We want to utilize our inputs as much as possible without wasted resources or money. That’s why timing of fall applications is so important.

2. Soil moisture. Adequate soil moisture is needed to convert ammonia to the more stable ammonium. Applying in too dry of soils means this process doesn’t happen, and more nitrogen is lost through denitrification. However, too wet of soil tends to lead to increased nitrification. Finding the balance of adequate moisture is a challenge, but will result in retaining as much nitrogen as possible.

3. Nitrification Inhibitors are an excellent idea for delaying nitrification, particularly if there is a possibility of the soil warming up after application. Products like N-serve can go a long way towards keeping nitrogen in the immobile ammonium form. In fact we recommend them for all fall applications on lighter soils. (This is something to budget out--if you are considering doing a lower rate fall application paired with an in-season application, maybe you forgo the N inhibitor to save money for the in season application. It really comes down to your budget and preferences.)

4. Check application depth and sealing. Verify that you are placing anhydrous deep enough in the soil; make sure it is getting into moisture. Equally as important is making sure that the application slot is getting adequately sealed. Since we are applying as a gas, an open slot allows that gas to escape before changing to a more immobile form within the soil. Our goal is to trap that gas pocket well below the surface of the soil until that gas has time to convert and bind to soil particles. If you smell gas a day after applying, its likely that you aren’t getting your slot sealed well. Make adjustments your knife or discs and trailing covering chains or discs to ensure the slots are sealing well.

5. Spring anhydrous is okay too. While it is advantageous to apply in fall from a time standpoint (frees us spring for planting prep, herbicide applications, etc.) as well as from a financial standpoint (fall anhydrous is generally cheaper than spring), there are some downsides to fall applications. Fall applications are much more prone to nitrogen loss with early spring warm-ups. The longer we have our nitrogen sitting in the ground, the greater the chance we will lose some. Many years we call this loss a wash for the time and cost benefits we get from fall applications. However, don’t lose sleep if you don’t get all your fall applications completed. Spring anhydrous is also highly effective with a few adjustments. Or even better, consider split applications. Research has shown applying a lower fall rate and pairing it with an early season or in season application can be the best of both worlds and highly efficient from a nutrient uptake standpoint.

Questions or concerns? Leave a comment below or send us an email!


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