Wet Soils, Yellow Crops and Options for Midseason Applications of Nitrogen Fertilizer

With the large rainfall events across many parts of Manitoba recently, some farmers are noticing yellowing in their crops and wondering if they should top up their fields with some more nitrogen fertilizer. Unfortunately, there are no easy rules to follow or large experimental datasets to refer to for making this type of decision.

The attached article by Dr. Don Flaten, University of Manitoba, and John Heard, Manitoba Agriculture, outlines some principles if considering midseason application of nitrogen fertilizer.

Wet Soils, Yellow Crops and Options for Midseason Applications of Nitrogen Fertilizer – June 2016

And remember….the first issue to consider is whether the crop yellowing is from N deficiency or simply flooding stress due to excess water. Applying N fertilizer onto crops that are suffering primarily from flooding stress could be a poor investment.

Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture

Visit Manitoba Agriculture website at http://www.gov.mb.ca/agriculture/crops/soil-fertility/ for more information on soil fertility.

 

Respond
Have a follow-up question?

Fall Nitrogen Applications

Fall nitrogen applications will be commencing shortly.  There is an important rule and several guidelines for legal and efficient use of nitrogen.

RULE: November 10.  Nitrogen and phosphorus applications must be made before this date to comply with regulations under The Nutrient Management Regulation of the Water Protection Act (C.C.S.M. c. W65).

GUIDELINES:

A)     Cool soil temperatures – when nitrogen is applied to cool soils, the biological conversion to the nitrate form is reduced.   The following table (adapted from Manitoba research by Tiessen et al) illustrates the dramatic impact of cool soils on slowing nitrification rates.  Conversely  on warm soils this conversion is rapid, and we wish this to happen during the growing season.  But once nitrogen is in the nitrate form it is vulnerable to leaching losses and denitrification under wet soil conditions.

Table 1.  The estimated rate of conversion of ammonia-N  from banded urea to nitrate-N. (Heard from Tiessen et al, 2003)

Picture1

Growers and agronomists can measure soil temperatures at the depth of injection.  Soil temperature at 2” depth under sod is posted for a number of Manitoba sites at MAFRD’s Ag-Weather Program website: http://tgs.gov.mb.ca/climate/SoilTemp.aspx

B)     Banding N in the ammonia form also slows conversion to nitrate.

C)      Nitrification inhibitors can slow this conversion. These include the DCD component in SuperU, nitrapyrin in eNtrench for urea or N-Serve for anhydrous ammonia.

D)      Controlled release products, like ESN,  slow the physical release of urea, which in turn slows this conversion to nitrate.

Following the 4R Approach – especially source, time and placement – will maximize performance of fall applied nitrogen fertilizer.

Submitted by:  John Heard, Crop Nutrition Specialist, MAFRD

Respond
Have a follow-up question?

Spray corn now – or fertilize more

Early season weeds in corn not only compete and reduce yield, but mean more nitrogen fertilizer is required to maintain good yields.  Many farmers recognize that today’s herbicides can provide excellent control – and some can control weeds at advanced stages. The tendency may be to delay applications so one application of herbicide gets all the weeds. But studies in Wisconsin and demonstrations in Manitoba show that even though weed control may be 100% in such fields, the nitrogen efficiency is much reduced.  Wisconsin studies showed that compared to weed-free fields, when control was delayed until weeds were 4”  and 12” tall, an extra 20 to 60 and 60 to 160 lb N/ac respectively was required for full yield.  So to optimize nitrogen efficiency in corn, control weeds early.

Submitted by:  John Heard, Crop Nutrition Specialist, MAFRD

Respond
Have a follow-up question?

Time to side dress corn is now

Many of the corn fields in Manitoba have emerged and for those fields that have not yet received their full complement of nitrogen fertilizer – now is a good time to make that application.  There is no need to wait until corn plants are large before side-dressing with anhydrous ammonia or UAN solution.  The time to apply is when the fields are suitable for traffic and injection.

One of our greater risks on non-tiled drained fields is that wet soil conditions in mid-June may hinder field applications of side dressed injected nitrogen.  Although alternatives are available, they come with some potential damage and reduction in nitrogen efficiency.  Broadcast urea to larger plants may leave some pellets in the whorl which cause  leaf burn.  Liquid 28-0-0 (UAN solution) may cause leaf burn when leaves are contacted.  Dribble banding reduces leaf area affected compared to broadcast application, although dribbles tend to run into the whorl of larger plants. Surface applications to moist soil is subject to volatilization loss so Agrotain treatment may be necessary.

Submitted by:  John Heard, Crop Nutrition Specialist, MAFRD

Respond
Have a follow-up question?

Still Lots of N Fertilizer Options when Seeding is Delayed

In a 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 compromised to advance seeding dates.

There are a wide variety of options for applying nitrogen fertilizer efficiently, which are discussed in the article by John Heard, Crop Nutrition Specialist with MAFRD, available at the following link:  http://www.gov.mb.ca/agriculture/crops/soil-fertility/n-fertilizer-options-when-seeding-delayed.html

 

Respond
Have a follow-up question?

Banded nitrogen with wide spaced seed rows

Question from a Subscriber of Crop Chatter:  I’m setting up a triple shoot air drill with wide (12.6 inch) spaced seed shanks. Each seed shank has a 3.5 inch paired row seed opener with a granular fertilizer placement tube to put granular fertilizer in the center of each paired row. Additionally, the drill has mid row banding shanks on 25.2″ spacing to apply NH3. I have a 3 compartment air tank.

For cereals, I will place the seed and phosphorus together through the paired row openers, with starter urea placed in the middle of each seed row through the granular fertilizer tubes. For canola, the seed and phosphorus will be placed together with ammonium sulphate (and possibly some urea if a fertilizer blend is used) in the center of each seed row. For soybeans, the seed and granular innoculant will be placed together and phosphorus will be placed in the seed row centers. NH3 will be applied for cereals and canola through the mid row shanks with 1″ openers. The NH3 will therefore be up to about 7″ away from the furthest placed seed.

I’m trying to determine how to best split the total nitrogen rate between urea and NH3. Since NH3 is cheaper and less handling than urea, my preference is to maximize NH3 use. Given that I have heavy clay soil:

1) How long it will take the furthest away plants to be able to access the NH3?
2) How much urea should be applied to keep the crop well suppied with nitrogen until all plants can access the NH3 band?

Answer (provided by John Heard, MAFRI Soil Nutrition Specialist)

Crop roots access nitrogen in mid-row bands in 2 ways:  roots growing  laterally can intercept the band and mid-row placed  ammonia converts to nitrate-N which then migrates as roots consume soil moisture.  Usually mid-row banded nitrogen is available for crop growth by the time it is needed.  Your seed-placed phosphorus fertilizer usually contains nitrogen to keep the seedling nourished.  But we hear on occasion that early season crop yellowing (MN deficiency?) is observed in the situations here – cool, heavy clay soil with wide spaced mid-row bands.  In years with warm, moist or dry soils, root access to bands will likely be quicker than this year.  Fortunately you have an option to place some urea in a band close to, but safely away from the seed.  I should think no more than 10-20% of the nitrogen requirement needs to be supplied there.

Respond
Have a follow-up question?

When is the perfect time to put nitrogen out on winter wheat?

If we get conditions where temperatures drop far enough below freezing at night, the soil will support ground application equipment until mid morning.  That way nitrogen is getting on early before much growth occurs.  Waiting until soils have warmed up risk having conditions too wet to allow traffic.  Early nitrogen is very important to encourage tillering of winter injured wheat or poor stands.

Establishment of red clover cover crops is improved with this frost-seeding approach.  Co-application of clover seed with nitrogen has been a successful practice in Ontario and when moist weather follows wheat harvest and can produce considerable nitrogen credits.  Details at:  http://www.gov.mb.ca/agriculture/soilwater/nutrient/fnm02s02.html  

Answer supplied by John Heard, MAFRI Crop Nutrition Specialist

Respond
Have a follow-up question?

Is the soil too dry to apply anhydrous ammonia?

Dry soils are a challenge to in-soil banded nitrogen application, especially anhydrous ammonia.  When anhydrous ammonia is injected into soil the ammonia (NH3) is dissolved in water and reacts to convert to ammonium (NH4+), which is positively charged and held by the cation exchange on the soil particles.

Soil moisture is needed to allow the ammonia to convert and be retained in the soil, however even in dry soils there is usually enough moisture present for this to occur.  The major problem with dry soils is the clods or lumps that form can prevent a good seal, allowing the ammonia to be lost through large voids between clods before dissolution in moisture occurs. Indeed, nitrogen losses on low moisture soils are caused more by poor physical soil structure (soil tilth) than by a lack of moisture to chemically react with ammonia.

Clay soils that are very dry will be cloddy or lumpy and may permit too much gaseous ammonia to escape. The zone of ammonia dissipation from the injection point is larger in dry soil, so although the soil may be difficult to work, deeper injection may actually be required.  Lighter textured soils will have better tilth than dry clay soils and will be more likely to produce a good seal to retain the ammonia.

Slot closure may be better on previously worked  than on uncultivated soils if the soil flows and seals better.  Such is not the case if soils were cloddy.  Some cereal crops were harvested almost 2 months ago and the moisture that has been received may be sufficient to provide good tilth.  Soil moisture and texture varies across the province, as does farm equipment.  The only way to assess your soil conditions is a test run with your applicator. An application pass without N will indicate whether soils are too cloddy and injection slot closure is inadequate. If after making a round with N, you can still smell ammonia from the previous application, make adjustments in depth or closure modifications.  Or wait for rainfall to improve soil structure.

For more information http://www.gov.mb.ca/agriculture/soilwater/nutrient/pdf/fer01s01.pdf

Respond
Have a follow-up question?