Thom Weir, Farmers Edge Senior Precision Agronomist
The last blog was dedicated to discussing drought and the history of droughts on the Prairies and Northern Great Plains over the last 100 years. I also discussed soil moisture and provided some ideas on how to manage soil moisture in a drought. In this blog, I will discuss nutrient management in drought scenarios. As we did previously, we will examine this topic through the lens of 4R Nutrient Stewardship.
This fall, the first key consideration when planning a fertilizer application is the Right Rate. The five keys to the Right Rate are:
- Get a Soil Test. You may be pleasantly surprised by the carryover levels.
- Get a Soil Test done to 60 cm (24 inches). Due to the extreme drought encountered across the Canadian Prairies and Northern Great Plains, there might be significant residual nitrogen at depths below 30 cm (12 inches). You should try to determine how much is present, as these nutrients will be considered when preparing a recommendation for next year.
- Consider using Management Zones and Variable Rate Applications this year. There may be significant variability across fields, as we have seen throughout the droughts over the last couple of years. This will result in nutrient removal and, therefore, residual nutrient levels.
- Get your testing done this fall. If you have dry soil, start testing early. Growers often hold off on testing until October, when temperatures drop to about 10oC (50oF), to ensure soil microbial activity has slowed and mineralization of nutrients has halted. The mineralization process requires moisture to take place, so if your soil is already dry, there is no need to wait. If your soils are moist with late summer or early fall precipitation, wait until the first of October for sampling.
- Set a realistic yield goal. In most areas, growers have encountered three consecutive dry years. 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. Remember, you can top up nitrogen rates in the spring if conditions change between now and springtime.
The next key consideration to make when reviewing a fertilizer application is the Right Place, which in drought conditions is in a band placed 6.5 – 8 cm (approx. 2.5 to 3 inches) deep.
Toward the end of the 1980s and the 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 “world-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 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, it was referred to as “deep banding” in western Canada. A subsequent observation was made during the droughts of 1988 and 1989. The fall banded products, either urea or anhydrous ammonia, strongly outperformed the industry standard of spring broadcasting. Further investigation discovered that the crop’s roots proliferated when they found an area rich in nutrients. Research has since determined that the optimum depth for a band is 6.5 – 8 cm (approx. 2.5 to 3 inches). To this day, this is still considered the blue-ribbon standard for applying nitrogen, especially under drought conditions.
In the 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 a banding operation. However, it should again be noted that the ideal depth of this band is 6.5 – 8 cm (approx. 2.5 to 3 inches). A 3.8 X 3.8 cm (1.5 X 1.5 inch) separation of seed to fertilizer, when seeding at 1.25 cm (0.5 inch) depth, your fertilizer depth would be 5 cm (2 inches). At this depth, there is a risk of volatilization losses. Worn fertilizer knives may reduce this further.
Note: most of the 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, plants with roots three inches deep did better than those whose roots were concentrated in the top inch.
As for the Right Time, fall fertilization seems to work very well under drought scenarios. The caveat here is that there needs to be enough moisture to allow for a banding operation of either urea or anhydrous ammonia to occur. Under dry conditions, many soils containing significant levels of clay will appear as hard clods when banding occurs. In addition, the soil may not seal behind the knives and cause volatilization losses.
The final key consideration to make this fall when reviewing a fertilizer application is the Right Source. 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 utilized 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 are magnified by drought.
- Banding fertilizer in the fall where possible.
- Bands should be 6.5 – 8 cm (approx. 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 and wonderful product, ask them if they can provide performance data (hopefully generated using 3rd party research). If they can, ask them if any of the tests were conducted under drought conditions. As I stated in the last blog, moisture is often the most limiting factor. I have not come across research results of additives and enhancers’ performance in drought conditions on the Canadian Prairies or Northern Plains. The other consideration that needs to be examined is the return on investment for new technologies and products. If a manufacturer has data that shows a five-percent yield increase on 60-bushel canola, it’s three bushels. However, if you calculate the yield increase on a 30-bushel crop, you only get a one-and-a-half-bushel 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 product performance data to get it registered by CFIA. If the company cannot produce reputable data, unfortunately, you are the Guinea Pig. And remember, at the end of most trials, the Guinea Pigs are discarded.
Questions? Connect with our agronomy team: Email Info@FarmersEdge.ca