Fall ammonia applications on dry soils

With rapid crop maturity and harvest many farmers will be looking to the next job on their list – fall fertilization. Typically, fall nitrogen is applied by 34-46% of Manitoba farms, and the most popular source is still anhydrous ammonia.

Last year in SW Manitoba, an inadvertent application of ammonia to excessively dry soil caused distress to adjacent landowners, so let’s review a few of the basics regarding N application.

Can soils be too dry for anhydrous ammonia?

Although soil moisture is low, it doesn’t take much moisture for the chemical reaction of ammonia (NH3) with H+ ions from water to convert to ammonium (NH4+).  This positively charged ammonium cation is then held on the exchange complex of clay and organic matter.

But dry soils do affect the physical closure of injection slots and may allow physical escape of ammonia gas. When soils are dry, big clods of soil may form and leave large channels for ammonia to move quickly and escape to the atmosphere. In those situations, ammonia loss can be substantial.

Clay soils that are very dry will be cloddy or lumpy and may permit too much gaseous ammonia to escape (Figure 1). 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. However, deep tillage of dry clay soils may simply produce larger clods. 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.

 

What can one do if soils are dry?

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.

Deeper application may help put the ammonia closer to moisture and prevent the dissipation zone from reaching the surface. In the cornbelt where high N rates are applied on 30” spaced shanks, recommendations for dry soils are to place ammonia 6-8” deep, whereas typical ammonia injection depths are 3-4” on the Prairies. Attempts to place ammonia so deep here on clay soils may just produce larger clods.

Modifications to injection knives may offer some help. In-crop ammonia application for corn often uses closing disks or sealing wings (“beaver tails”) on the knives to aid coverage/closure of injection slots.

However, in most cases the farmer is best to wait for rainfall to improve soil tilth.

How do I know losses are unacceptable?

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.

The “white puffs of smoke” are not ammonia gas, but clouds of water vapour. As long as ammonia smells do not persist after application, these white clouds should not be a major concern.

Will fall ammonia banding make my soils drier?

Fall banding can have contrasting effects of soil moisture. Under very dry conditions where snow-cover is limited, the loss of standing stubble through this banding tillage reduces snow trap on the field and may leave the field susceptible to evaporative losses.

However, in areas where snow cover is more reliable, fall banding may provide better moisture than a spring banded application. Spring banding can dry the seedbed, reducing available moisture and seedbed quality.

Additional information on fall N application is posted at:https://www.gov.mb.ca/agriculture/crops/soil-fertility/pubs/fer01s01.pdf

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Volatilization of surface applied urea/UAN

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist
Surface broadcasting of nitrogen (N) fertilizers has become popular to increase operational efficiency – increasing the speed of seeding and reducing risk of seed injury.  But, in a dry spring with limited rain prospects, growers may choose not to till and avoid further drying out seedbeds.  Then growers must consider the risks of nitrogen volatilization loss and take precautions when risk is high.
Volatilization of ammonia (NH3) from urea or the urea portion of UAN (28-0-0) affected by several factors and can be increased under specific situations.
For more details on the risk factors and ways to minimize losses, see full .pdf 
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
 
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Seed Placed Fertilizer Cautions for Canola

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist

Spring 2018 has brought many questions about seedplaced fertilizer rates for canola.  Several factors are causing concern:

  • Drier soils – which increase the risk of seed toxicity
  • Desire to apply sufficient P to meet crop removal – since many fields have seen decreasing P levels due to high yield.  P removal is about 1 lb P2O5/bu, so high yield potential fields are looking at high P replacement rates.
  • Increased use in low disturbance, low seedbed utilization (SBU) drills.  Many new openers are arriving on the scene, which are “close-to-seed” sidebanding for which one may need to consider as seedplaced.
  • Desire by growers to reduce seeding rates for cost savings.  Most research studies investigating seedplaced fertilizer injury were seeded at some 150 seed/m2, about double what some farmers are now targeting.
For more detailed analysis on the issue, see the full text in .pdf format 
 
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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.

Picture1

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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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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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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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

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