Special nutrient management required in drought years

Canola bashed and eaten - Wind, drought and flea beetles have impared this canola crop near Wilcox, Sask., making nutrient future nutrient decisions more challenging. Fertilizer prills can be seen eroded to the soil's surface of this crop.  |  Mike Raine photo

My previous column discussed drought and the history of droughts on the Prairies and the northern U.S. Plains over the last 100 years.

This column will discuss nutrient management in drought scenarios.

We will look at this topic through the lens of 4-R nutrient stewardship; right rate, right place, right time, right source.

The first key consideration to make when considering a fertilizer application is the right rate. The five considerations of the right rate are:

1. Get a soil test done. You may be pleasantly surprised with carry-over levels.

2. Get a soil test done to 60 centimetres (24 inches). Because of the extreme drought encountered across the Canadian Prairies and the U.S. northern Great Plains, there might be significant residual nitrogen at depths below 30 cm. You should try and determine how much is there because these nutrients will be considered when preparing a recommendation for next year.

3. Consider using management zones and variable rate applications. There may be significant variability across fields because after a drought like we have encountered over the last couple years, we have seen a wide variation in yields across fields and this will relate to nutrient removal and therefore residual nutrient levels.

4. Get your testing done this fall. If your soil is very dry, waiting for the middle of October when the soil temperature falls to around 10 C may not be necessary. Waiting is done to make sure soil microbial activity has slowed and mineralization of nutrients will not be occurring. The mineralization process requires moisture to occur so things will be at a stand-still when the soil is dry. If your soils are moist with late summer or fall precipitation, wait at least till the first of October for sampling.

5. Set a realistic yield goal. We have just come off three very dry years in some areas. Is it realistic to fertilize for an above-average crop if you are going into the season with significant soil moisture deficits? You may not be able to produce the yields you were used to producing five years ago. And you can top up nitrogen rates in spring if conditions change between now and then.

The next key consideration to make this fall when considering a fertilizer application is the right place.

First, a history lesson. Back in the last half of the 1980s and first half of the 1990s there was a migration from the use of ammonium nitrate (34-0-0) to urea (46-0-0) and anhydrous ammonia (82-0-0).

New large-scale fertilizer plants were being built in Western Canada to manufacture anhydrous ammonia and urea. Soil researchers were tasked with comparing the performance of ammonium nitrate to these “new” products. In those days the most common method of application was broadcasting.

One of the early observations that was made was that anhydrous ammonia performed better than either ammonium nitrate or urea applied at the same nitrogen rate. Researchers dug deeper and found that when either ammonium nitrate or urea was banded at an equivalent depth, they performed equally. This was the birth of banding — or in those days referred to as deep banding in Western Canada.

A subsequent observation was made during the droughts of 1988 and 89. The fall-banded products — either urea or anhydrous ammonia — performed very well when compared to the industry standard of spring broadcasting.

When I say performed well, we are talking 40 percent-plus or better. Further investigation found that the crop’s roots proliferate when they found an area rich in nutrients.

Research has since determined that the optimum depth for a band is 6.5 – eight cm (2.5 to three inches).

This performance observation has continued to this day with a band 6.5 – eight cm is considered the blue-ribbon standard for applying nitrogen, especially under drought conditions.

So the right place in drought conditions is in a band placed 6.5 to eight cm deep. This can be done in the fall or spring.

In spring, a banding operation can be made but under drought conditions, the moisture loss due to banding may cause yield losses. A fertilizer application at seeding is usually banded in. However, achieving the ideal depth of may prove difficult. A 3.8 x 3.8 cm (1.5xX 1.5 inch) separation of seed to fertilizer, when seeding at 1.25 cm (0.5 inch) depth, your fertilizer depth would be five cm (two inches), which is less than the optimal 6.5 to eight cm. At this depth, there is a risk of volatilization losses. Worn fertilizer knives may reduce this further.

Note that most of this research was done with wheat or barley. A broadcast application with or without shallow incorporation caused crop roots to proliferate near the surface. When drought conditions increased in June, the plants with the roots three inches deep did better than those whose roots were concentrated in the top inch.

For tight time, I could easily say refer to above. Fall fertilization seems to work very well in the fall under drought scenarios. The caveat is there needs to be enough moisture to allow for a banding operation of either urea or anhydrous ammonia.

Under dry conditions, many soils containing significant levels of clay will come up as hard clods when banding. As well, the soil may not seal behind the knives and cause volatilization losses.

The final key consideration to make this fall when considering a fertilizer application is the right source. The key considerations remain the same as with general recommendations when considering fall applications. Ammonium-based products (urea, anhydrous ammonia, ammonium sulphate) are all recommended. The broadcast applications of products with urease and/or nitrification inhibitors may result in the nitrogen being stranded at or near the soil surface. This may not be effectively used as the roots grow deep to find moisture. The performance of ESN improves in a band.

In summary, under drought conditions, the best management practices include:

  • Soil sampling to determine nutrient carryover.
  • Set realistic yield goals for next year’s crops under your expected moisture conditions.
  • Use management zones as the amount of variability in a field is magnified by drought.
  • Banding fertilizer in the fall where possible.
  • Bands should be 6.5 to eight cm (2.5 to 3 inches) below the soil surface.
  • Fall banding works best with ammonium-based fertilizers.

Remember when a salesperson approaches you with a new product promising incredible performance ask him for performance data, hopefully generated using third party research.

If the salesperson has the data, ask them if any of the work was done under drought conditions. The fact is, moisture is often our most limiting factor.

I have not seen research results of additives and enhancers performance in drought conditions on the Canadian Prairies or the U.S. northern Plains.

The other consideration is return on investment for new technologies and new products. If a manufacturer has data that shows a five percent yield increase on a 60 bushel canola crop, that equals three bu. However, if we calculate the yield increase on a 30 bu. crop, we only get a 1.5 bu. increase, which may not cover the cost of application. Be leery of a one-size-fits-all approach and broad statements about product performance.

Since April 1, 2013, companies are no longer required to provide performance data of a product to get it registered. If the company cannot produce reputable data, you are the guinea pig. And remember, at the end of most trials, the guinea pigs are sacrificed.

Thom Weir PAg is a certified crop advisor and professional agrologist in the Yorkton, Sask., region. You can reach him at thom.weir@farmersedge.ca.


For more content related to drought management visit The Dry Times, where you can find a collection of stories from our family of publications as well as links to external resources to support your decisions through these difficult times.

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