Options For Applying Nitrogen Fertilizer In A Wet, Late Spring

Farmers can be justifiably concerned about their fertilization practices when extensive flooding occurs in the Red River Valley. Not only does flooding directly impact soil fertility status, but other production practices, such as seeding date and preseeding tillage, will be altered and traditional fertilizer application methods may need adjustment.

In a wet spring when seeding is delayed, field operations should be minimized to permit seeding as soon as possible. Preplant applications of N, in particular may be omitted in order to advance seeding dates.

The clay textured soils and the moist climate in the Red River Valley, however, create the opportunity for a wide variety of options for applying nitrogen fertilizer efficiently during a wet, late spring. Some suitable options for applying nitrogen fertilizer under these conditions are listed below.

1) Preplant Band Immediately Prior To Seeding

Nitrogen fertilizer may be banded immediately prior to seeding using all nitrogen forms, including anhydrous ammonia (82-0-0) or urea (46-0-0), provided that the fertilizer is separated from the seed. Anhydrous ammonia should be placed at least 4" below the soil surface, and ideally the crop should be seeded perpendicular to anhydrous ammonia bands. There is no need to delay seeding after application if anhydrous ammonia is placed at recommended depths, especially in moist clay soils. The average efficiency for spring banding is rated higher than spring broadcasting. However, these efficiency ratings do not consider the potentially negative impact of preplant banding on seeding date and seedbed quality.

2) Preplant Broadcast

Tillage during conventional seeding operations is generally sufficient to incorporate either urea (46-0-0) or UAN solution (28-0-0). If these fertilizers are left on the soil surface, there is a risk that nitrogen will be lost due to volatilization or "gassing off." The average efficiency for broadcasting is rated lower than spring banding, but similar to fall banding for Manitoba soils. However, as mentioned previously these efficiency ratings do not consider the impact of preplant banding on seeding date and seedbed quality.

3)Seed Row Application

Typically, up to half of the cereal crops N needs may be met with seed row application, depending on the spreading width of seed and fertilizer, row spacing, soil type and moisture levels at seeding. Moist clay soils, for example, allow higher rates of N to be placed with the seed, compared to dry or sandy soils. Remaining N could be delayed until your spring soil test results are available. Refer to Table 7 in the Soil Fertility Guide for specific safe ratio of seed placed N.

4) Side Band At Seeding

A crop's full requirement for nitrogen fertilizer might be applied as a band beside the seed row if adequate separation exists between the fertilizer and the seed row. N must be placed at least 1 inch to the side of the seed row if solution or dry N is used, and 2-3 inches below and beside the row if anhydrous ammonia is used. Several side banding openers are available to provide adequate nitrogen separation.

5) Broadcast Immediately After Seeding, Prior To Crop Emergence

Solid or liquid forms of nitrogen could be broadcast and harrowed in after seeding as part of seedbed firming and leveling. Harrowing can provide some incorporation and reduce the risk of volatilization or "gassing off". High rates of urea-N(>90lb N per acre) applied without incorporation, especially on drill-seeded fields, may cause seedling damage to sensitive crops such as canola.

6) Band Immediately After Seeding, Prior To Crop Emergence

Limited research has indicated that post seeding banding of anhydrous ammonia may have some advantages over top dressing in terms of cost and efficiency. Research was conducted on heavy clay soils seeded with diskers or air seeders. If such a strategy is attempted, ensure that anhydrous ammonia is placed with a narrow knife or low disturbance opener to minimize disruption of the seedbed. Also, ensure that the anhydrous ammonia is applied at the recommended depth to minimize the potential for seedling damage and to prevent ammonia escape from the trench.

7) Top-Dress After Crop Emergence

Top-dressing allows for uncomplicated, quick seeding; it is also an efficient method of applying nitrogen fertilizer if rainfall is received soon after application, which is common in the spring in the Red River Valley. In addition, this method of application may allow farmers to soil test after seeding to determine the availability of fall applied N.

Ammonium nitrate was the most reliable source for top-dressing, but is no longer available for prairie growers. However, urea's average performance is still acceptable, especially with good soil contact and favourable moisture (see Table 1). Band stripping of dry N will minimize surface contact and may reduce volatilization potential.

The performance of broadcast UAN solution may not be as high as for other forms of N (see Table 1). However, the performance of UAN solution is improved if applied with spoke-wheel injection or dribble application.

Table 1. Effect Of Pre- And Post-Emergent Application Of Several N Fertilizers* On Yield Of Barley In Manitoba
(Average of 5 experiments conducted by University of Manitoba)

Fertilizer Source Yield of Barley (bu/ac)

Time of Application

At Seeding 2 weeks after emergence 4 weeks after emergence
Ammonium nitrate (34-0-0) 57 54 58
Urea (46-0-0) 59 54 56
UAN solution (28-0-0) broadcast 54 51 50

* Fertilizer application rate was 52 lb N per acre in all treatments. check yield without N fertilizer was 42 bu/ac.
** In other experiments in Manitoba, post-emergent application of UAN solution was similar in efficiency to application at planting.

The success of top dressing N fertilizer is affected by many factors, If rainfall is not received after broadcasting, any form of N fertilizer may remain stranded at the surface, and be vulnerable to volatilization loss. Following are conditions affecting the potential for N loss through volatilization.

Table 2. Conditions That Affect Volatilization Losses Of N Fertilizer

High Loss Potential Low Loss Potential
moist conditions, followed by rapid drying
high soil temperatures
high soil pH (>pH 7.5)
high lime content in surface soil
coarse soil texture (sandy)
low organic matter content
high amount of surface residue (zero till)
dry conditions, followed by rainfall
low soil temperatures
low pH (<7.5)
no lime at soil surface
fine textured soil (clay)
high organic matter content
conventional tillage

The risk of volatilization loss of urea or the urea portion of UAN solution (28-0-0) can be reduced through the use of Agrotain urease inhibitor. This additive will delay volatilization of urea for up to 2 - weeks, thereby increasing the probability of receiving sufficient rain for incorporation.

Early applications will produce the greatest yield benefit since crop yield potential is determined early. Ideally N should be applied to cereals at or before the 3-5 leaf stage and prior to bolting of canola. Later applications may result in increases in protein rather than yield. When a substantial rate of N fertilizer is planned for a top-dressed application, farmers should provide some nitrogen at seeding (please refer to Option #3). This ensures a supply of nitrogen for the young plant should top-dressing be delayed by unfavourable weather.

Information compiled by
Manitoba Agriculture
Dr. Don Flaten, School of Agriculture, Faculty of Agricultural and Food Sciences, University of Manitoba
Dr. Geza Racz, Department of Soil Science, Faculty of Agricultural and Food Sciences, University of Manitoba