Apply last fall’s missed nitrogen this spring

It’s not too late to apply last fall’s N this month, if you missed your regular 2019 window there are spring solutions available

According to the Agriculture Canada precipitation map, large areas of all three prairie provinces received 115 to more than 200 percent of normal rainfall in September and October last fall.

Created on Nov. 1, the map was prepared in conjunction with Natural Resources Canada, Environment Canada and provincial and private agencies.

It tells farmers what they already know. Mother Nature gave many of them a kick in the gut last fall. Combines that should have been put away in anticipation of the 2020 harvest are currently back in the field cleaning up the shabby remains of the 2019 crop. Once in the bin, some of these crops will require attention to salvage what value remains.

And once the 2019 crop is binned, then it’s time for fall nitrogen, six months behind schedule for those producers who normally apply in the fall. In Manitoba, for example, fall nitrogen application is the primary practice for 45 percent of wheat, 34 percent of canola and 32 percent of corn. Obviously warm, breezy weather is on everyone’s minds these weeks — that and snow.

To help farmers work through this problem, a new fact sheet was recently prepared titled Fertilization Considerations after an Unusually Wet Fall: Challenges and Opportunities.

The publication was prepared by crop fertility specialist John Heard with Manitoba Agriculture and Resource development and soil scientist Don Flaten from the University of Manitoba. The following is a synopsis of that fact sheet.

Many farmers need to apply an unusually large proportion of their fertilizer this spring and summer. This shift in timing creates significant challenges. The report says advances in fertilizer sources and application methods provide good options to help farmers deal with those challenges.

Early seeding is important to optimize crop yield. Producers want to apply nitrogen fertilizer efficiently without delaying the seeding operation. In order to achieve that objective, the fertilizer source, fertilizer placement and fertilizer timing must be managed carefully.

Fortunately, there are timing and placement options other than fall broadcast or banded nitrogen to meet the needs of the crop. In addition, combinations of new sources and new application equipment give farmers more options than ever for spring and midseason nitrogen applications:

  • Fertilizer application equipment such as high clearance sprayers and floaters can apply 28-0-0 in dribble or directed bands immediately after planting or in established crops.
  • Fertilizer additives, such as urease inhibitors, can be mixed with conventional fertilizers or purchased as enhanced efficiency fertilizers, such as SuperU. These additives delay the conversion of urea to ammonia and reduce the risk of gaseous losses due to volatilization of surface applied urea or UAN solutions.
  • Several enhanced efficiency fertilizers or additives contain nitrification inhibitors, such as N-Serve for ammonia and eNtrench for urea and UAN, and DCD (SuperU and Agrotain Plus) UAN. These slow the process of ammonium conversion to nitrate, decreasing potential leaching and denitrification losses under wet conditions such as those expected for spring 2020.
  • Controlled release fertilizers such as ESN fertilizer, which has a polymer coating, can reduce the toxicity of seed-row placed urea applied at planting. Higher rates of nitrogen can be applied safely in the seed row.

There are five spring and summer options for the timing and placement of nitrogen:

Pre-plant banding — Banding nitrogen below the soil surface tends to be the most efficient form of application. Banding protects the ammonia portion from gaseous losses by volatilization. Banding limits contact between the fertilizer and the soil micro-organisms, thus reducing immobilization of both ammonium and nitrate. Banding also slows the conversion of urea to ammonium and ammonium to nitrate. This reduces loss by denitrification and leaching. Ideally, bands should not be disturbed by pre-seeding tillage or seeding operations.

All forms of nitrogen fertilizer usually perform well when applied as a spring pre-plant band, provided the fertilizer is at least two inches away from the seed. Anhydrous ammonia should be placed at least four inches below the surface. If possible, seeding should be perpendicular to NH3 bands. Urea should be banded as deep as possible for seed safety. It should be at least two inches deeper than the seed and, on an angle, to seed rows. There’s no need to delay seeding after NH3 or urea application if it’s placed at recommended depths, especially on moist clay soils.

Where spring tillage will be required to manage ruts left by harvest, spring banding with a cultivator-style air seeder may accomplish both jobs. Likewise, many farmers have low disturbance disc drill seeders that could be used to band granular fertilizer before or after seeding.

Surface applications immediately before or after seeding — Broadcasting is a fast method of applying fertilizers, with some applicators covering 1,000 acres per day. However, urea or UAN sources of nitrogen can be lost by volatilization unless or until they are incorporated into the soil with tillage or moved into the soil with precipitation if the soil is dry enough.

Nitrogen losses occur not only in the fall but again in the spring because a wet fall is typically followed by a wet spring. There is a poor probability of snow melt infiltration, which leads to overland runoff and ponding. Broadcast N converts more quickly to nitrate than banded nitrogen. This increases the risk of leaching on coarse-textured sandy soils. It increases the risk of denitrification on poorly drained, fine-textured clay soils.

Tillage during conventional seeding operations is generally sufficient to incorporate urea or UAN solution to reduce volatilization. However, harrowing, shallow vertical tillage and low-disturbance seeding may allow volatilization loss of urea or UAN.

If either ammonium or nitrate sources are in close contact with crop residues, they may be subject to immobilization as the residues decompose. Micro-organisms will consume nitrogen from the soil or fertilizer as they decompose crop residues that are low in nitrogen, such as cereal residues. High rates of broadcast urea nitrogen applied without incorporation on drill-seeded fields may concentrate pellets in the seed-furrow and cause seedling damage to sensitive crops such as canola.

Where fields are rutted and tillage is required, it might be logical to first broadcast fertilizer. Cultivators and discs incorporate fertilizer to a depth of three or four inches. Harrowing or shallow vertical tillage may not be sufficient for full incorporation. Volatilization losses have been observed at shallow incorporation depths.

Because of the high potential for volatilization and immobilization, surface applications of nitrogen tend to be less efficient than banded applications. Efficiency is lower on high pH soil because high pH encourages the production of ammonia gas.

While less efficient than banded or incorporated, surface nitrogen applications without incorporation may be appropriate for fertilization of forages, winter cereals and for post-emergent nitrogen delivery. Dribble banding to reduce contact with crop residues is a better choice than broadcast urea for surface applications. Volatilization losses with dribble banded UAN are lower than with urea because UAN provides a portion of the nitrogen as nitrate and because UAN does not increase initial pH at the application site to the same extent as urea.

Both factors reduce the proportion of nitrogen present as ammonia, thus reducing volatilization. Use of a dribble-band rather than a spray application limits contact between the fertilizer and crop residue, thus reducing immobilization. In Manitoba field studies, surface dribble-banded applications of UAN were nearly as effective as in-soil banded applications.

Another option to reduce urea or UAN volatilization loss from broadcast fertilizer is to use a urease inhibitor such as Agrotain or SuperU. Urease inhibitors slow the conversion of urea to ammonium, allowing more time for the urea to move into the soil before being converted into ammonium and ammonia. Slower conversion reduces the concentration of ammonia at the soil surface, reducing the rate of volatilization.

The economic benefit of urease inhibitors will depend on the relative risk of volatilization loss and the cost of both the fertilizer and the inhibitor. Because volatilization losses from UAN are generally lower than from urea, the benefit of using the urease inhibitor is likely to be lower with UAN than with urea.

While a higher rate may be required to compensate for the reduced efficiency for surface applications, this may be a practical compromise, particularly for producers who can’t access specialized equipment for in-soil fertilizer placement.

Placement of fertilizer in the seed row is an attractive option when nitrogen can’t be side-banded or mid-row banded at planting. If fertilizer is placed directly with the seed, it eliminates the extra expense and soil disturbance required to side-band or mid-row band the nitrogen. Seed-row placement helps reduce losses.

Applying excess nitrogen with the seed can lead to seedling damage due to salt and ammonia toxicity. Such damage delays crop emergence, reduces yield, limits crop response to nitrogen fertilizer and reduces nitrogen efficiency. This increases weed competition and delays crop maturity, which increases risk of damage from fall frosts.

Side-banding or mid-row banding at seeding — Banding of nitrogen to the side and below the seed lowers the risk of toxicity compared to seed-placing. Many commercial and home-manufactured openers have been designed for one-pass seeding and fertilizing.

Often the entire nitrogen needs of the crop can be met through sideband placement. Research has shown that one inch to the side and one inch below the seed may not be sufficient separation for crop safety, especially for sensitive crops such as canola. Therefore, if the entire nitrogen supply is to be applied, the side band should be at least two inches from the seed row for solution or dry fertilizer and at least two to three inches from the seed-row for anhydrous ammonia. Mid-row banding nitrogen between every second seed row at seeding has the greatest degree of seed safety.

Liquid fertilizer is convenient for one-pass systems because equipment is easier to work with and cheaper to modify than equipment for granular or ammonia application. Anhydrous ammonia is a relatively low-cost nitrogen source, but concerns exist as to its seed safety for application in a one-pass system. It can be safely applied using side-band or mid-row band equipment, as long as the seed-fertilizer separation is at least two to three inches.

Good opener wear-ability, good soil tilth, good moisture conditions and reasonable ground speed are important to ensure that seed and fertilizer separation is maintained. Wing-tip injection of anhydrous ammonia on sweep openers has performed well for cereals on heavier soils. However, with the shallower depths for canola or flax, there may not be sufficient soil coverage to prevent ammonia escape to the surface.

The latest seeders do a good job of side-banding or mid-row placement, but the cost of equipment can be high. Draft requirement and seed bed disturbance may increase and trash clearance may become a problem. However, the benefits of combining seeding and fertilization into one operation can be significant and pay long-term dividends.

Banding nitrogen immediately after seeding — A small amount of research and practice indicates that banding anhydrous immediately after seeding may have some advantages over topdressing in terms of cost and efficiency. This research was conducted years ago on heavy clay soils previously seeded with discers or air seeders.

If such a strategy is attempted, ensure that anhydrous ammonia is placed perpendicular to the direction of seeding, using a low disturbance opener to minimize destruction of the seed bed. Also ensure that the anhydrous ammonia is injected at the recommended depth to minimize the potential for seedling damage and to prevent ammonia escape from the trench.

With very precise RTK guidance, some farmers have successfully banded between seeded rows after seeding. This is only practical in row spacings at least 10 inches wide and with low disturbance equipment that can band fertilizer into the soil with minimal stand disruption or injury.

Producers may want to delay applying some nitrogen until they have a better estimate of the yield potential or because of constraints on the amount of nitrogen they can apply before or during seeding.

Historically, midseason application of all or part of a crop’s nitrogen fertilizer has not produced higher yields than pre-plant or one-pass seed with fertilizer. However, new fertilizer products and practices have improved the efficiency of post-planting applications as a complement to applications at or near planting.

Recent research on split nitrogen with urease-treated urea produced the highest spring wheat yields when 25 to 50 percent of it was split-applied at stem elongation. However, more than five millimetres of rain were received within five days of application.

Broadcast top-dressing nitrogen after crop emergence can be an efficient method of applying if it rains soon after. 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 applications if it’s dribble-banded or injected using coulter applicators after crop emergence. Conversely, applying UAN in a full-coverage spray may result in leaf burning and significant losses. Ideally, post-emergent nitrogen should be applied to cereals no later than heading and to canola before bolting.

Long-season, wide-row crops such as corn and sunflowers have numerous opportunities for in-season application. This includes top dressing, side dressed banding between rows and surface banding with a Y-drop application of UAN.

Regardless of which source and placement is used for midseason application, early season requirements must also be met. Therefore, a substantial amount should also be applied at or near planting in situations where soil supplies are low or to deal with the risk of adverse weather that could delay post-seeding applications.

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