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Les Henry: Anhydrous ammonia and the 4Rs

Time to bring back what should be the cheapest form of nitrogen fertilizer

Almost all farm press of late that talks about fertilizer use emphasizes the 4R concept. That means that we will take each nutrient and decide what is the “right” source to use, what is the “right” application rate, what is the “right” placement and what is the “right” time to apply that nutrient.

The nutrient we usually spend the most money on and apply at the highest rate is nitrogen. Nitrogen is also susceptible to loss mechanisms such as leaching below the root zone of the crop or denitrification or gassing off.

One way to apply nitrogen is in gas form, as anhydrous ammonia.

History of anhydrous

Anhydrous ammonia first made a brief appearance in Western Canada in the 1950s. At that time nitrogen application rates were low and little stubble cropping was done — it was before its time.

When the big boom of the 1970s arrived, it was time for dealers and manufacturers to get serious about developing the anhydrous ammonia market. This was met with some pushback that suggested that anhydrous ammonia would wreck the land.

At the University of Saskatchewan, we conducted considerable research to prove that all of the claims suggesting anhydrous ammonia was bad for the soil were false.

One of the main criticisms was that anhydrous ammonia would do away with earthworms. I said “What earthworms?” as we had few or none at that time. In recent years, with the development of zero-till agriculture and much higher rates of anhydrous ammonia, we find that the two are really quite compatible. Anhydrous ammonia does not damage earthworms.

Applying anhydrous ammonia does not fumigate the land. The anhydrous that is released at the point of injection forms a small pear shape, two to three inches in diameter. The rest of the soil is unaffected.

When anhydrous ammonia first came into use it was considered unfair competition by those that only sold urea. Urea was broadcast, and ammonia, of course, was deep banded. John Harapiak at the then-Westco Fertilizer conducted extensive research with deep banding urea in the fall. He found that anhydrous ammonia and urea were essentially equal when placed equally. In fact, his data said that the difference in yield between broadcasting and deep banding urea was enough to pay for the fertilizer.

Anhydrous ammonia is a dangerous good and commands considerable respect in use and handling. However, gasoline is also a dangerous good that requires considerable respect in handling.

In the past few years anhydrous ammonia use in our area has declined sharply. The product is still available, but support for equipment to apply is limited and there seems to be little price differential.

The 4Rs on my farm

For cereal crops and canola on my little patch of ground, I consider the 4Rs of nitrogen to be as follows.

Source: Anhydrous ammonia should be the cheapest source. No matter what nitrogen source we use, the manufacturing starting point is anhydrous ammonia. The product is 82 per cent nitrogen. In comparison, urea is only 46 per cent nitrogen. It does not take a very sharp pencil to figure the difference in transporting similar amounts of nitrogen in anhydrous ammonia or urea form.

Rate: The rate is determined by the reserve of soil moisture that is present and, ideally, by a soil test. If the soil is fully supplied with water and the crop is wheat or canola the correct rate is about 100 pounds of nitrogen per acre (on all except the saline acres and the land recently broken from pig pasture). For malt barley the rate is lowered, to avoid overly high protein.

If the soil has little or no subsoil storage, the right rate is much lower — perhaps as low as zero. For the 2002 wheat crop there was no subsoil moisture. We used no anhydrous and harvested 18 bu/ac of wheat with 5.7 inches of rain from May to July.

The right rate is closely tied to the reserve of soil moisture at seeding. Often, that data is available at freeze-up. If the soil is full of water then, it will still be full of water in spring.

Placement: The correct placement of ammonia is deep banding at a depth of three to four inches.

Timing: Most years the best timing is late fall. Anhydrous ammonia is its own nitrification inhibitor. The concentration of ammonia in the immediate injection zone is high, and that in itself will inhibit the transfer of ammonia to nitrate. If the operation is done in late fall and at sufficient depth there is very little risk of loss of any kind.

Spring application before seeding can create a timing crunch and the physical disturbance of the seed bed can result in dry soil that will inhibit crop germination.

In theory, nitrogen timing should be related to the timing of the crop’s nitrogen uptake. For irrigation farmers that’s easy — just put 28-0-0 in the water. For dryland farmers, in-season application of nitrogen relies on a timely rain after application (not very predictable).

Many now apply all their nitrogen at seeding as a side or midrow band. That works great as long as it is not too shallow. And it makes for a lot of material handling in a narrow seeding window.

It is my wish that we see more dealers be more aggressive with anhydrous ammonia. I still think it is a great option.

About the author


J.L.(Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms at Dundurn, Sask. He recently finished a second printing of “Henry’s Handbook of Soil and Water,” a book that mixes the basics and practical aspects of soil, fertilizer and farming. Les will cover the shipping and GST for “Grainews” readers. Simply send a cheque for $50 to Henry Perspectives, 143 Tucker Cres., Saskatoon, Sask., S7H 3H7, and he will dispatch a signed book.


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