Spring Options for Applying Nitrogen Fertilizer in 2020
With the wet conditions and delayed harvest experienced in parts of Manitoba in fall 2019, very few farmers were able to complete their fall fertilization program. Since early seeding is important for optimizing crop yield, producers will be looking for ways to apply their nitrogen (N) requirements efficiently without delaying the seeding operation. In addition, soil reserves of N are variable, and although fertilizer prices are relatively modest, optimizing N use efficiency is important. In order to achieve these objectives for a spring fertilization program, the fertilizer source, placement and timing must be managed to minimize losses of fertilizer N to the environment and optimize crop access to the fertilizer.
Recent surveys of Manitoba farmers indicate that a high portion (32-45%) routinely apply fall N predominantly in a banded placement. However, many other spring placement options are available and are routinely used by farmers.
Pre-plant Banding – Banding N in concentrated rows below the soil surface tends to be the most efficient form of application under western Canadian conditions. Placing the fertilizer below the soil surface protects the ammonia portion from volatilization losses. Placing the fertilizer in a band limits the contact between the fertilizer and the soil microorganisms, reducing immobilization of both ammonium and nitrate. Banding also slows the conversion of urea to ammonium and ammonium to nitrate, which can reduce losses by denitrification and leaching. Ideally, bands should not be disturbed by pre-seeding tillage or seeding operations.
Surface Applications Immediately Before or After Seeding – Broadcasting is a very fast method of applying fertilizers. However, urea or UAN solution sources of N can be lost by volatilization until they are incorporated or moved into the soil with precipitation. Tillage during conventional seeding operations is generally enough to incorporate urea or UAN solution to reduce volatilization.
Placement in the Seed-row – Placement of fertilizer in the seed-row is an attractive option, since it eliminates an extra pass for fertilizer application. If the fertilizer is placed directly with the seed, it eliminates the extra expense, draft requirements and soil disturbance required to side-band the fertilizer requirements. Seed-row placement is a form of banding, so it is efficient in terms of reducing N losses. Applying excess nitrogen with the seed, however, can lead to seedling damage due to combination of salt and ammonia toxicity. Such damage often reduces crop yields, limits crop response to nitrogen fertilizer and reduces nitrogen use efficiency.
Side-banding or Mid-row Banding at Seeding – Banding of N to the side and below the seed will decrease the risk of ammonia toxicity compared to seed-placing. Many commercial and home-manufactured openers have been designed for one-pass seeding and fertilizing. These include simple systems where fluid N is dispensed through a tube on the seed-opener and mixed with the soil as it falls back over the seed, combined seed and fertilizer boots which place the N in a band separated from the seed, and systems with separate openers for side-band or mid-row placement. Often the entire N needs of the crop can be met through sideband placement, but Manitoba research has shown that placement 1” to the side and 1” below may NOT be enough separation for crop safety. Therefore, if the entire N needs are to be applied, the side band should be at least 2” from the seed row for solution or dry fertilizer and at least 2-3” from the seed-row for anhydrous ammonia. Mid-row banding the N between every second row at seeding maintains the greatest degree of seed safety. Less soil disturbance, and hence more moisture retention, would be achieved with a disk type mid-row bander unit compared to a shank-type.
Banding Nitrogen Immediately After Seeding – Limited research and practice indicates that banding NH3 immediately after seeding may have some advantages over topdressing 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 NH3 is placed perpendicular to the direction of seeding, using a narrow knife or low disturbance opener to minimize destruction of the seedbed. Also ensure that NH3 is injected at the recommended depth to minimize the potential for seedling damage and to prevent ammonia escape from the trench.
Post Emergence or Midseason Applications – Historically, under Manitoba conditions, applying all or part of a crop’s N requirement after emergence does not produce higher yields than pre-plant or one-pass applications. However, in some cases, producers may not be able band their N fertilizer prior to seeding due to time limitations or risk of poor seedbed quality. In other cases, producers may want to delay applying a portion of their N fertilizer until they have better estimate of their crop’s yield potential.
In these cases, top-dressing is often a reasonably efficient method of applying N fertilizer if rain falls soon after application, which is common in the spring in much of Manitoba. However, post-seeding surface applications will be subject to the same considerations as surface applications prior to seeding. UAN is well-adapted to use for post-seeding N applications if it is dribble-banded or injected using spoke-wheel or coulter applicators after crop emergence. Conversely, applying UAN in a full-coverage spray may result in leaf burning and significant losses of N.
Ideally, post-emergent N should be applied to cereals at or before the 3-5 leaf stage. Recent research on split N application produced highest spring wheat yield when 25-50% of the N was split applied at stem elongation – when more than 5mm of rain was received within 5 days of application.
Enhanced Efficiency Fertilizers (EEF) – Several EEFs are nitrification inhibitors, which tend to slow the process where ammonium is converted to nitrate, decreasing potential leaching and denitrification losses under wet conditions. These include nitrapyrin (N-Serve for NH3 and eNtrench for urea and UAN) and DCD (SuperU and Agrotain Plus for UAN). Similarly, the controlled release N such as ESN slows the accumulation of nitrate-N. Such products may be beneficial when nitrate-N is exposed to prolonged excessively wet conditions and when crop uptake is low.
View MWBGA’s Spring Nitrogen Application Options fact sheet here.
Article adapted by Mallorie Lewarne, MWBGA Agronomy Extension Specialist. Original article, “Spring Options for Applying N Fertilizer” written by John Heard, Manitoba Agriculture and Resource Development, and Dr. Don Flaten, University of Manitoba.
To read the full article on minimizing fertilizer loss to the environment, optimizing crop access to fertilizer, and spring N application options, click here.