Fertilizer Implications in a Dry Spring for Winter Cereal Crops

Prior to the precipitation that started Wednesday, May 25th, it had been unusually dry this spring (Figure 1 below) and there are nitrogen fertilization implications.


Figure 1. Rainfall received in Carman, 2016.

Farmers and agronomists may be wondering about the fate of previously applied surface fertilizer. The 2 main concerns would have been stranding at the soil surface where it is isolated from the crop root zone, and volatilization loss.

Rainfall is the only solution for the positional stranding at the soil surface. For spring seeded crops this rainfall will likely have moved N into the root zone before any malnutrition of the seedling.  However surface applied N to fall rye and winter wheat may have been stranded during the main yield building period, since both crops are at the boot stage now (Figure 2 below).  So in the Carman area, topdressed N applied after April 17 was probably stranded.  Nitrogen moving into the root zone now will contribute more to protein than yield.

N Uptake by Wheat for Yield & Protein

Figure 2. Nitrogen uptake pattern by wheat (from C. Jones., Montana State University)

The other concern is of volatilization loss of surface applied N. But much of the surface applied N to spring seeded crops was onto dry soil – and we have had several  field demonstrations to measure volatilization loss using dosimeter tubes (see photo below). In the cases we have followed, the soil surface must have been dry enough to prevent measurable hydrolysis (where the urea molecule is cleaved into carbon dioxide and 2 ammonia molecules).  In fact urea pellets were observed intact for several weeks on the soil surface.  So unless a light shower had been received, I anticipate losses were minimal.  Where some soil moisture was present, the losses would have proceeded until the soil surface dried up.

figure 3

Figure 3. Dosimeter tubes to monitor ammonia loss from surface applied urea or UAN. Note intact urea pellets at soil surface some 10 days after application. There were no ammonia losses.


The best way to sense any N shortage in the crop is comparing to a N Rich Strip. Many farmers no longer overlap fertilizer so this is difficult to detect. If there is little to no colour difference between a N rich strip and the general field, then losses are probably minimal.

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

For more information on soil fertility, visit Manitoba Agriculture’s website at http://www.gov.mb.ca/agriculture/crops/soil-fertility/index.html
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Surface N Applications & Dry Soils

Planting is proceeding at full tilt and some questions are arising about surface N applications.  When urea forms of N are surface applied, they are vulnerable to hydrolysis (the cleaving of the urea molecule with water) and subsequent losses of ammonia gas (NH3) called “volatilization.  This is a well established risk  and risk factors are well known, and more information can be in the article Volatilization Losses From Surface Applied Nitrogen on the MAFRD website.

Conditions favouring high volatilization potential are:

  • high soil temperatures
  • moist conditions, followed by rapid drying
  • windy conditions
  • high soil pH (>pH 7.5)
  • high lime content in surface soil
  • coarse soil texture (sandy)
  • low organic matter content
  • high amounts of surface residue (e.g. Zero tillage)
  • nitrogen source: urea>UAN solution
  • UAN application: broadcast UAN> dribble or strip UAN

Our observations in Manitoba have been that urea or UAN solution (28-0-0) applied to bone dry soil actually suffers little volatilization loss  since there is little moisture to drive hydrolysis. At this point with dry conditions forecasted, the riskiest situation may be by exposing your applied N to enough soil moisture to start the volatilization process – such as applying immediately after some soil disturbance like seeding or secondary tillage.  Likewise, very shallow incorporation through seeding or harrowing may start this process.  Light rains of 1/10″ may also be enough to start this volatilization process, yet inadequate to incorporate the urea molecule.  Generally rainfall of ¼ to 0.4” is considered sufficient to incorporate surface urea or UAN.

If you must apply urea or UAN to moist soils or in other high risk situations, a NBPT urease inhibitor like Agrotain is recommended.  Although volatilization losses on already dry soil surfaces are usually low neither is this surface N doing any good until rainfall is received.  A strategy of waiting until imminent rainfall may still be a preferred option.

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

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Qn: Where did all the weeds come from in that corn field?

Farmers are usually well advised to “control weeds early and often” in corn fields. Although many of today’s herbicide tolerant crops and herbicides can control weeds at almost any stage, it is early season competition that reduces nitrogen use efficiency. University of Wisconsin researchers compared weed free corn to delayed weed control. Spraying when weeds were 4” and 12” tall, required an additional 20-60 and 65-160 lb nitrogen /ac, respectively, to produce corn yields equal to weed free plots.

In our 2014 Crop Diagnostic School lesson, corn fertilized with 100 lb nitrogen/ac yielded 145 bu/ac with season-long weed control, 15 bu/ac less when spraying 4” tall weeds and 60 bu/ac less when spraying 12” tall weeds (Figure 1). Unsprayed corn yielded 9 bu/ac. Conversely, with no added nitrogen but early and consistent weed control, the corn yielded 95 bu/ac.

John Heard in corn field

Figure 1. Corn to left in background with full, but late, control of weeds suffered extreme nitrogen deficiency.

However, there are warranted exceptions to maintaining all growing vegetation from growing in corn fields. Many corn fields in southern Manitoba are currently seeded with a wheat or oat companion crop (see Figures 2 & 3). These fields tend to be at high risk of wind erosion: sandy textured, following potato or other low residue crops. Cereals seeded at or prior to corn can then establish and produce early season ground cover to minimize soil erosion and sand blasting injury to young corn seedlings.

Figure 2

Figure 2. A nurse crop of wheat emerging in mid-May, ahead of the corn crop in Winkler area.

oats in corn field

Figure 3. A nurse crop of oats emerging in late May, in Carman area corn crop, prior to spraying for removal.

For more information on erosion and cover crops visit MAFRD’s website at: http://www.gov.mb.ca/agriculture/environment/soil-management/soil-management-guide/soil-erosion.html

Answer Submitted by John Heard, Crop Nutrition Specialist, MAFRD


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Apply your Nitrogen Stamp – Assess Losses and Sufficiency for Your Crop

Submitted by John Heard, Crop Nutrition Specialist, Manitoba Agriculture

With the excessive rainfall and standing water in some Manitoba fields, some agronomists may be asked to assess possible N losses. If applied N had already converted to nitrate (NO3) form it is subject to leaching on sandy soils and denitrification on poorly drained and heavier textured soils.

In many cases it is not too late to apply your “Nitrogen Rich Strip” or N Stamp” that can serve as a reference when one wants to assess potential losses and yield penalties. Nitrogen Rich Strips are usually applied with field equipment and run across the field to encompass a range of soil types, drainage, etc. Simple differences in colour and growth between the field and this strip usually indicate a lack of N for field yield potential. When applied before or at seeding such strips should be 150-200% of the base field N rate. A number of devices and sensors (like chlorophyll sensors, NDVI or GreenSeeker) can be used to quantify such a difference and estimate in-season N applications for a variety of crops.

Nitrogen Ramp Calibration Strips or N Stamps can be simply applied by hand after seeding into fields. Details on applying the N Ramp Calibration Strip are available at: http://www.gov.mb.ca/agriculture/crops/soil-fertility/nitrogen-ramp-calibration-strips-in-manitoba.html

N Stamps are simpler – generally 30, 60 and 90 lb N/ac hand applied within a 20ft x 20ft (6m x 6m) cells. We are applying these in several wheat fields to test the abilities of UAVs or drones to detect N differences in fields. To try this out simply weigh 258, 517 and 775 g of urea into bags and hand apply to the 20’ x 20’ plot. We treat our urea with NBPT to minimize losses to volatilization. Observe differences in colour and growth. If none are seen mid-season, then the applied N was likely sufficient for yield.



20 ‘

 20’ 0 N check


30lb N/ac          =  258 g urea


60lb N/ac            = 517 g urea

90lb N/ac          = 775 g urea



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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).


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)


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

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My corn is quickly approaching knee-high in height and with the wet conditions it’s been a struggle to get on the field. What are some N application options?

Nitrogen application is critical to corn as it nears the knee high stage.  Up to this point, the plant has consumed  little N but will be taking up 2.5 lb/ac/day as it approaches tasselling.

Broadcasting granular fertilizer such as urea can cause leaf scorching from those granules that end up in the whorl.  Likewise, dribble UAN application can cause substantial leaf burn since droplets either run either off the leaf or into the whorl. And corn may be too large or soil too wet to allow side-dress injection of  ammonia or UAN into the ground.

A safe option is to dribble UAN (28-0-0) using drop pipes so it contacts the ground and avoids the leaves.  This simply means plumbing the high clearance sprayer with nozzles every 30” (rather than the current 20” for pesticides) and attaching flexible hoses to direct liquid to the soil.  In the USA, one brand of  the off-the-shelf units called Y-Drop Applicators have been so popular they are sold out.  If soils are moist and temperatures hot, you should consider adding Agrotain to minimize volatilization loss from the applied fertilizer.

Submitted by:  John Heard, Crop Nutrition Specialist, MAFRD

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GOT YELLOW CORN? Using Tissue & Soil Analysis to Confirm Nutrient Deficiency

Not only are soybeans turning yellow in Manitoba, but corn is as well.   So how do you confirm a nutrient deficiency is causing the yellowing?

John Lee of AGVISE Laboratories provided MAFRD staff last year (2013) with the below information on how to properly determine if nutrient deficiencies are playing a role in the ‘yellowing’ corn seen across Manitoba.   It is a great article so thank you to John Lee!

Using Tissue and Soil Analysis to Confirm Nutrient Deficiency in Corn

A cool, cloudy spring with excessive moisture has affected many areas.  One effect of these conditions has been yellow corn from Manitoba to South Dakota.  Using plant tissue analysis along with soil analysis can help determine if the yellow corn is a result of sulfur or nitrogen deficiency.

AGVISE staff recently worked with a local grower to help him determine why one of his corn fields was yellow while the adjacent neighbor’s field was dark green.  Tissue and soil samples were collected from the yellow corn field and also from the adjacent corn field planted the same day.  The concentration of sulfur in the plant tissue from the yellow corn field was well below the sufficiency range established for sulfur at this stage of growth.  The nitrogen concentration in the yellow corn was good and in the middle of the sufficiency range for this stage of growth.  A tissue sample from the adjacent corn field with dark green color was also tested and found to have sulfur and nitrogen levels well within the sufficiency ranges (see tissue and soil test results and pictures of corn at http://www.agvise.com/wp-content/uploads/2013/06/S-defcorn-AGVISEExample20132.pdf).  There were also a large difference in the soil nitrate and sulfate sulfur levels in the soil samples from the yellow field and the adjacent green field.

The soil type in these fields is a sandy loam which is subject to leaching of sulfur and nitrogen with excessive rainfall like this spring.  The yellow field did not have sulfur fertilizer applied this spring while the adjacent dark green corn did have sulfur fertilizer broadcast and tilled in before planting.  The grower was planning on sidedressing the yellow corn with nitrogen fertilizer, but but now with the additional information from the tissue and soil tests, he is going to include some sulfur fertilizer in the sidedress application as well on this sandy loam soil.

This is just one example of how using tissue analysis along with soil analysis in season can help figure out if symptoms are being caused by a nutrient deficiency and which nutrient is the main cause of the symptoms.

Note:  If agronomists/producers send suspected nutrient deficiencies to MAFRD’s Crop Diagnostic Lab, please send samples for tissue and soil analysis simultaneously to an appropriate laboratory.  Then follow up with Crop Diagnostic Lab on the results from the tissue and soil analysis.

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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

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My winter wheat has been fertilized with nitrogen, but is so thin it is going to be sprayed out and seeded to soybeans. Will the extra nitrogen harm the soybeans?

Answer provided by John Heard, MAFRD Crop Nutrition Specialist

Our initial experiences of soybeans and high nitrogen soils in Manitoba were negative. High soil N tends to inhibit nodulation while at the same time this nitrogen tends to grow slightly larger vegetative plants. However after flowering that nitrogen is often insufficient to provide full yield and protein potential for the crop. So we adopted a thumb rule that if soils had more than 60-75 lb nitrate-N/acre, producers should consider growing a crop other than soybeans.   The other crops should benefit more from the N than the soybeans, which would still take up the nitrogen but may not express full yield and protein. Nitrogen was also seen to trigger iron deficiency chlorosis in soybeans grown in wetter, high lime soils.

But more recently farmers and agronomists have observed that soybeans may perform well on some high N soils. This may be because soybeans have been grown more often and a native reserve of rhizobium exists in many of these cropped soils. With industry partners (AGVISE Labs and ToneAg Consulting) we made observations at 13 field demonstrations in 2013 where high soil N levels were simulated with N application (Heard et al, 2013). Our observations were:

  • Nitrogen at 50-100 lb N/ac reduced nodulation at all sites, but most severely at the virgin or first time soybean sites. Nodule numbers were still generally sufficient on those fields with a previous history of soybeans (Figure 1).
  • Few sites were harvested for yield, but nitrogen affect was more severe on the first year soybeans (reduced yield or lower protein).

Figure 1: Average rhizobium nodules per root from 13 demonstrations in 2013.


So if one needs to replant soybeans on a field already fertilized with nitrogen consider:

  • Whether well nodulated soybeans have been grown in the past.
  • Treating fields with a history of soybeans as virgin fields by applying full rate of inoculant
  • Even if fields have high N in the spring, soybeans will largely deplete those reserves during the season

One may still wish to avoid planting soybeans if it is a virgin field or if there is risk of iron deficiency chlorosis.

There was no advantage to supplementing properly nodulated soybeans with additional nitrogen at these sites. In US studies, additional nitrogen appears warranted “sometimes” when yields are very high (>65 bu/ac) or when nodulation failures occur due to acid soil, drought or other adverse weather conditions.


Heard, J., J. Lee and R. Tone. 2013. Nitrogen and soybeans: Friends, foes or just wasted fertility? Manitoba Agropnomists Conference 2013.



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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


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