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Thursday, April 23, 2015

Anhydrous Ammonia Applications

Fabian Fernandez, Nutrient management specialist

Anhydrous ammonia (AA) is one of the most widely used nitrogen (N) fertilizer source in Minnesota and the Midwest. Some of the reasons for its importance include the fact that this source is by far the most concentrated N fertilizer with 82% N (less weight of fertilizer per unit of N); it is readily available since AA is used in the manufacture of many commercial N fertilizers; it can be applied several weeks before planting with less N loss potential than other N sources; and most importantly AA normally represents a less expensive source of N. Some of the drawbacks of AA include the need for special facilities to store this gas as pressurized liquid, and special equipment to transport and applied this fertilizer; the application of AA can be slower than that of some other N sources; and because AA is released as a gas, it can pose a risk to human health if not handled properly. Every year as farmers start applying AA, invariably I get asked similar questions which I will try to address today.

What is a good soil moisture condition for anhydrous ammonia application, and can I apply it deeper to compensate for less-than-ideal soil conditions?
When AA is applied it quickly reacts with organic matter, clay particles, free hydrogen ions, and most importantly with soil water that prevent volatilization of ammonia. Other factors that can influence the size and shape of the retention zone include the rate of application and the equipment or method of application, soil texture, and soil structure. Typically, AA stays in an oval-shaped retention zone of about 2 to 5 inches in diameter.

Anhydrous ammonia losses to the atmosphere at the time of application are mostly dependent on soil moisture and depth of injection. Ideal soil conditions are around 15 to 20% moisture. Within these moisture levels a fine-textured soil, such as a silty clay loam soil, feels slightly moist. If pressed in the palm of your hands it will form a weak ball with rough surfaces that crumbles under pressure and will not leave water stains on your hands.

Moisture conditions across the state vary significantly this spring. If soil conditions are too dry, ammonia can escape because it will travels too much distance in the soil to react with soil water. This is rarely a problem in fine-textured soils. This year some fields look dry, but there is good amount of moisture just below the soil surface.

If soils are too wet, the knife track might not sealed properly creating a direct conduit for ammonia to escape to the soil surface. This is definitely a concern given the wet soil conditions in the state this spring. When soils are slightly above or below the ideal moisture conditions, increasing application depth can reduce the risk of ammonia loss. An adequate application depth under ideal moisture conditions is approximately 6 inches for fine-textured soil and 8 inches for coarser textured soils (sandy soils). For wet soils, sometimes increasing the application depth is not sufficient to minimize ammonia losses, and it is recommended to also use some type of device behind the knife to close the slot created by the knife. Always the best test to determine if a proper seal is obtained is to go back to the application zone and smell. If ammonia can be smelled for a while after the application, that’s clear evidence that ammonia losses are occurring. Also, when considering AA applications in wet conditions, beware that likely you will be creating compaction and smearing of soil surfaces. That’s not a trivial issue especially if it turns dry later in the season and crop roots were not able to grow well because of compaction created at this time.

Is anhydrous ammonia application between every-other-row as effective as application between every row?
The answer to this question is, yes. This application requires less horsepower to pull the application equipment across the field, less knives to be maintained, and research has demonstrated no yield difference compared to the same rate of N applied between every row in standard 30-inch row spacing. Every-other-row applications are most effective at sidedress time where the location of the rows is known or for pre-plant applications using RTK guidance to ensure each corn row will have access to the applied N.  

Another potential advantage to applying AA in every-other-row is that effectively, the rate of N is doubled in the application zone compared to an application in every row. As explained earlier AA reacts with water and free-hydrogen ions and creates a temporary alkaline (high pH) zone which inhibits bacterial transformation of ammonium to nitrate. The higher the rate of application in a localized zone, the longer the inhibition effect remains. Retaining N longer in the ammonium form can be especially important for early N applications or when the potential for N loss due to leaching or denitrification is high.

How long do I have to wait after anhydrous ammonia application to plant corn?
The only risk of planting soon after AA application is if seeds fall within the ammonia retention zone. To avoid seedling injury separation in time or space can be important. Under ideal soil moisture conditions and proper application depth of a typical agronomic rate normally there is little risk of seedling injury even if planted on top of the application zone right after AA application. That said, this can be risky and I would not recommend 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 would recommend applying AA on an angle to the direction of planting to minimize the potential for planting on top of the AA band. If application conditions are less than ideal and you have no RTK guidance to ensure a safe distance from the AA band, then waiting 3 to 5 days before planting is typically enough time to reduce the risk of seedling injury.

How long after anhydrous ammonia application can I till the soil?
The answer to this question is similar to the previous question in the sense that it depends on depth of application and soil conditions. Under ideal soil conditions and typical application depth, shallow tillage can be done immediately after application. Under some conditions shallow tillage may also help seal the knife tracks. The reaction of ammonia to ammonium is very rapid in the soil and deep tillage that would disturbed the ammonia retention zone normally will cause no problems if done a few days after the application. As mentioned earlier, if you smell ammonia after doing a tillage pass it would indicate that the conversion of ammonia to ammonium is not complete and you should wait to till the soil.   

Does anhydrous ammonia application compacts soils?
The answer to this question is, no. This is a myth that has been circulating for many years. Research has shown that repeated application of AA caused no soil compaction (as measured by bulk density of the soil) in the plow layer or below the plow layer. Similarly, AA applications have not shown to reduce soil organic matter.   

Does anhydrous ammonia application change chemical conditions in the soil and affect soil microbes?
As explained earlier, the conversion of ammonia to ammonium creates temporary alkaline conditions in the ammonia retention zone. However, the process of nitrification (conversion of ammonium to nitrate) is an acid forming reaction and the overall effect of AA applications is a reduction in soil pH. It is important to recognize, though, that this acidification is not unique to AA, but other N sources have similar effects on soil pH.

Application of AA is toxic to microorganisms in the ammonia retention zone and can drastically reduce populations of bacteria and fungi at the time of application. Studies have shown, however, that the effect is highly localized (within a few inches of the release point) and temporary as the retention zone becomes re-colonized after several weeks.

Fabián G. Fernández

New Irrigation Resources

The new Irrigation Extension website is up and running, and we have been able to add some new resources, and update some of the past resources.
Now that spring has sprung, one of the most powerful tools for maximizing irrigated yield is uniform application of irrigation water.  Testing uniformity every few years is a low cost way to make sure that your water is going where you want it. On a pivot with 15 foot nozzle spacing, one bad nozzle 1000 feet from the center can influence the yield on over 2 acres. That one bad nozzle (that costs about $5 to replace) could cost you over $600 in lost yield.
Below is a quick tutorial on irrigation uniformity testing.

A Quick Test to See Whether Your Small Grains Seed or Emerging Seedlings is Still Alive.

With air temperatures dropping down into the high teens overnight, I have fielded a number of calls already this morning with the question whether the earlier seeded wheat, barley, oats (or any crop for that matter) will make it, especially if the ground is frozen solid.

The fastest way to tell is to dig up some seed or seedlings and place them on a wetted-down paper towel at room temperature.  Within 24 hours you should see elongation of the coleoptile of the seedlings.  With seed that had not germinated yet, you may have to wait another day before you see a radicle and coleoptile appear.  If the seed and the germ are damaged by frost they will turn to mush within 24 hours at room temperature.  If the crop had already emerged, you can simply cut the above ground leaf material and place the seedling on the wetted-down paper towel and wait for new growth to elongate. 

PS) Ensure that the paper towel remains moist throughout the duration of the experiment.

Photo 1: Germinated wheat seed with adventitious roots pointing down and coleoptile pointing up. The radicle is hidden between the adventitious roots.

Tuesday, April 21, 2015

Forage Quarterly - Spring 2015

Dear Forage Producer,

The University of Minnesota Forage Team is proud to announce the third edition of the Forage Quarterly. Since spring is here, this issues focuses on establishment and early season management of forage production systems. In this edition we highlight seeding strategies, weed management, cover crops, insect control and identification.

We would like to take this time to highlight the contributors to this edition:

  • Bradley Heins, Ph.D. Assistant Professor. Expertise: Organic Dairy Production. Email:
  • Bruce Potter. Assistant Extension Professor. Expertise: Integrated Pest Mgt, crops, and forages. Email:
  • Craig Sheaffer, Ph.D. Professor. Expertise: Alfalfa, forage, and sustainable cropping systems. Email:
  • Deborah Samac, Ph.D. Research Plant Pathologist. USDA. Expertise: Disease resistance mechanisms in alfalfa.
  • Doug Holen. Regional Extension Educator. Expertise: Crops, small-grains, and forages. Email:
  • Jim Paulson. Regional Extension Educator. Expertise: Dairy nutrition,forages, grazing and organic production. Email:
  • M. Scott Wells, Ph.D. Assistant Professor. Expertise: Forages and cropping systems. Email:
  • Reagan Noland. Graduate Research Assistant. Expertise: forages, cropping systems, and precision agriculture. Email:
  • Roger Becker, Ph.D. Professor. Expertise: Agronomy and weed science. Email:

University of Minnesota Forage Team

In this issue
Alfalfa Assessment: Factors Leading to Winter Injury
Alfalfa Establishment: A Pathway to Increased Yield
Preparing for Successful Alfalfa/Grass Production
Using Herbicides to Establish Alfalfa
Aphanomyces Root Rot of Alfalfa Widespread Distribution of Race 2
Alfalfa Insects: What to Look for, How and When</a>

Click to read the Spring 2015 newsletter.

Click to read past issues of the Forage Quarterly.


University of Minnesota Extension Forage Team

Sunday, April 19, 2015

Assessing Damage From In-Furrow or Pop-Up Starter Fertilizer for Corn

By Daniel Kaiser
Extension Nutrient Management Specialist

I have been fielding more questions on seed placed fertilizer in areas where rainfall has been sparse this spring and soils are dry. In my previous post I discussed the use of in-furrow starter fertilizer. Placing fertilizer on the seed can help speed up early plant growth but also can substantially reduce stand if a fertilizer is over-applied or soils are dry. How dry is too dry? That is a good question and the answer depends on the soil corn is being planted in. For medium and fine textured soils, the risk of damage typically is lessened when the soil moisture content is 25% or greater.

Thursday, April 16, 2015

New bulletin helps growers manage the rotation from alfalfa to corn

Jeff Coulter, University of Minnesota

Crops that follow alfalfa usually benefit from reduced or eliminated nitrogen requirement from fertilizer or manure, increased yield potential compared to following other crops, and reduced pest pressure. A new Extension bulletin describes management practices for alfalfa termination and the two subsequent corn crops that will help growers utilize the benefits of alfalfa:

Wednesday, April 15, 2015

How Deep Dare I Drill Wheat, Barley and Oats Down to Find Moisture?

Ideally we like you to seed wheat, barley, and oats at 1.5 to 2 inches of depth.  The idea is that the seed should be placed deep enough to have access to adequate moisture yet shallow enough to emerge as quickly as possible. Seeds too close to the surface absorb moisture but are at risk of dying because roots cannot reach moisture quickly enough to sustain the germination and seedling growth.  Deeper seeding can reduce stand density and plant vigor because the inability of the coleoptile to reach the surface. 

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