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Risks of broadcasting nitrogen fertilizer sources

By Rigas Karamanos Ph.D, P.Ag

Broadcasting was the traditional approach to applying nitrogen fertilizer on the Prairies. However, research conducted in the 1970s and 1980s by private industry and universities across Western Canada has indicated the only reason anhydrous ammonia worked better than urea was because it was banded. This led to the banding of dry fertilizers. Deep banding became the “golden standard” on the Prairies. However, broadcasting has gained momentum in the last few years.

So, What Has Changed? 

Due to the large farm size, many growers are looking to urea broadcasting for improved operational efficiencies, including completing seeding in a shorter time. This hastened seeding can lead to better agronomic results. For example, research in southern Alberta has demonstrated delaying seeding past May 1 can lead to daily yield losses of 0.6% to 1.7% depending on the crop. Therefore, completing seeding before this date can result in greater yields. Further, recent research has shown urea and urea ammonium nitrate (UAN) placed less than two inches below the soil surface results in losses higher and equal to broadcast applications. However, deep banding urea and (UAN) at 2” and below is still superior to broadcast and shallow banding. 

Of course, broadcasting nitrogen fertilizers does not come without risks, which are associated with the conditions under which broadcasting takes place. Let’s examine those conditions.

Fall Broadcasting of Nitrogen Fertilizer

Traditionally, the formula for successful fall fertilization has included the following elements:

  1. ammonium form of nitrogen (anhydrous ammonia or urea), 
  2. deep band fertilizer application method (spacing and depth), 
  3. cool soil temperatures (10 oC or less),
  4. proper field selection,
  5. use of enhanced efficiency fertilizers. 

Research at Montana State University demonstrated in cold weather, nitrogen is at risk of loss. When treated with a urease inhibitor, such as AGROTAIN®, nitrogen loss of urea to ammonia volatilization was reduced by two-thirds compared to untreated urea.

Broadcasting urea on snow has always been an issue and remains a debated subject. Western Cooperative Fertilizers Ltd. (Westco) demonstrated this practice was only effective under a very specific set of soil and climatic conditions. These specific conditions include: a two-to-four-inch layer of newly fallen, fluffy snow on a previously snow-free field, with a period of mild weather following the snowfall when urea is broadcast applied, and urea pellets are dissolving and moving completely through the snow cover in a droplet of melted snow while penetrating through any thatch layer to establish good soil contact. These ideal conditions will seldom if ever, exist in most areas of the Prairies. Therefore, the application of urea on snow is not recommended. Westco trials conducted on very wet fields, fields in which the soil froze in a wet condition, fields with compacted, drifted or crusted snow, or fields with more than four inches of fresh snow cover consistently resulted in lower yields than when the urea was broadcast applied under snow-free conditions. To minimize losses, application of urea fertilizer through the snow should be avoided since fertilizer applied in this manner is more likely to be lost.

Research conducted at the University of Saskatchewan in the 1980s showed about 35% of autumn-applied fertilizer nitrogen was lost via denitrification and 7–20% became immobilized the following spring. The potential denitrification rates were markedly higher under zero tillage and the population of denitrifiers were up to six times higher than in the conventional tillage fields. Crop residues doubled the gaseous nitrogen losses. Temperatures above 5°C did not alter denitrification rates nor did a wide range of mineral nitrogen. Recent research demonstrates the use of fall broadcasting of urea stabilized with both a urease and nitrification inhibitor (SUPERU® fertilizer), minimized these losses and canola yields over 11 trials were equal to those obtained with spring deep banding.

Spring Broadcasting of Nitrogen Fertilizer

In unusually wet springs, losses from spring broadcasting of urea-based fertilizers are primarily due to denitrification. Otherwise, losses are primarily due to the volatilization of ammonia through the process of urea hydrolysis. These losses are minimized if the application of urea is followed by at least eight-tenths of an inch (2 cm) of rain or irrigation but can potentially increase under lower water regimes. Stabilizing urea with a urease inhibitor has been shown in 17 trials5 to reduce volatilization in broadcast urea and result in similar yields with those obtained with deep banded urea.

References:

1Ross McKenzie – Alberta Agriculture (retired) The Western Producer | www.producer.com | February 9, 2012

2Rochette et al., 2009. Agriculture and Agri-Food Canada.

3The underlying data was provided by North Dakota State University under Research Trial Financial Support Agreements with Koch Agronomic Services, LLC. Neither these institutions, nor the individual researchers referenced, endorse or recommend any product or service. Improvements in yield and nutrient use efficiency may not be observed in all cases.

4Aulakh, M.S and Rennie, D.A. 1986. Soil and Tillage Research, 7: 157-171

5Karamanos, R.E. et al. 2017. 2017, The Role of Enhanced Efficiency Fertilizers in Fall and Spring Nitrogen Placement, Managing Global Resources for a Secure Future, International ASA/CSSA/SSSA Annual Meetings, 22-25 October, Tampa, FL.

Rigas Karamanos Ph.D, P.Ag, FCSA, is a senior agronomist at Koch Fertilizer Canada. Rigas’ extensive career in agriculture in both the academic and private industry sector. Notably, he was awarded a fellowship in the Canadian Society of Agronomy In 2013 and was inducted into the Saskatchewan Hall of Fame in 2015. Rigas can be contacted at rigas.karamanos@kochind.com.