Is it too early for fall soil sampling?

Currently the traditional and most reliable method of measuring available N for the crop is the nitrate soil test. Fall sampling is most common, and to be effective, it should reflect the amount of N available at planting time. Manitoba recommendations have traditionally been to “delay sampling until soils have cooled to 5oC” so that all the N that will mineralize during the fall will be detected. This has historically been in early to mid October.

But earlier fall sampling may be desirable for number of reasons:

  • sampling is more likely to be done
  • analysis is available for fall fertilizer prescriptions and N application
  • sampling before tillage gives more consistent /reliable sample depths
  • volunteer crop regrowth is less likely to hide available N from test
  • can be used as an audit of the soil’s N supplying ability (after taking into account starting soil N, applied N and N removal) Between 1999 and 2000 we evaluated the effect of early vs later sampling at 8 Manitoba locations on cereal stubble (Table 1). On average soil nitrate levels did not vary, considering that our sampling error within the plots were considered to be 10 lb N/ac. If we had been waiting for average soil temperatures to drop to 5oC, we would have delayed sampling until mid October.
  • Table 1. Mean soil nitrate levels of 8 MB sites.
Sampling date Soil nitrate-N lb/ac in 0-24” Average soil temperature at 4” (1999-2000)
  Mean Carman Brandon
Early Sept 49 16o C
Mid Sept 53 12.5o C 11.5oC
Early Oct 47 7.3o C 8o C
Mid Oct 53 6.6o C 6o C
Early Nov 44 5.3o C 3.7o C
April 51  
May 60  

Soil nitrate levels did start to increase rapidly once spring sampling was delayed into May, due to mineralization in warm soils.

There were 2 instances where fall N levels did change from early fall sampling:

  • 2” of rain on a sandy soil in late October leached some 20 lb N/ac below the 24” sampling depth
  • Aggressive fall tillage (2x) on a high organic matter loam soil, increased soil N by some 25 lb N/ac

So early fall sampling is generally reliable on cereal stubble, but there remain known environmental and management factors that can still influence soil nitrate levels.

But soil sampling early just to exploit a cheap labour force before the school year starts, should not be a deciding factor (Figure 1).

OLYMPUS DIGITAL CAMERA

Figure 1. Hand sampling to 24” may be considered inhumane depending on soil conditions.

Reference:

Heard, J and J. Lee. 2001 The Influence of Sampling Time on Fall Soil Nitrate Levels. Manitoba Agronomist Conf. http://www.umanitoba.ca/faculties/afs/MAC_proceedings/2001/pdf/heard4.pdf

 

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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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When Should I Swath My Canola?

Staging canola for swathing or pre-harvest desiccation is critical to maintain high quality seed and maintain yield. Ideal swath timing is when 60% of seeds on the main stem have turned colour, meaning 60% of all the main stem seeds are showing some form of colour (yellow, brown, black) other than green.

For 60% seed colour change, the bottom third of the main stem of the plant will have totally brown/black to purplish seeds, the middle third will have turned, or be showing some spots of colour, and the top third are green. The green seeds must be firm and should roll between your fingers without squishing. At this stage, the average moisture content is about 30%.

Producers are reminded that more than one area in a field will need to be assessed for seed colour change. Relying on a visual assessment of canola pod colour alone will not provide an accurate estimate of crop stage. In many cases, the outside of the pod colour can turn brownish yellow but seeds inside may still be green.

Swathing

Delaying swathing of canola until the 60% seed colour change stage usually allows for:

  • Improved yield and quality through increased seed size
  • Reducing green seed
  • Higher oil content
  • Minimizing economic shattering losses

Earlier swathing tends to lock in green chlorophyll in underdeveloped seeds, reducing oil content and potentially causing marketing issues. Canola can be swathed in the 30-40% seed colour change stage to manage a large number of acres ripening at the same time, but producers should be aware that swathing at this stage can cause yield losses up to 8%.

Dry growing conditions and damaging weather have impacted canola development across Manitoba in 2018. Evaluating canola fields for evenness and uniformity is important to selecting the right time to swath or desiccate the crop. If growth conditions allowed large patches of delayed emergence, or hail set back crop development, estimating the patch size and managing the crop according to the largest percentage area is a good recommended practice.

Pre-Harvest Aid/Desiccation

Glyphosate, Heat and Diquat herbicides are all registered for use as either a pre-harvest aid or a desiccant on canola. Check the labels or the Guide to Crop Protection (https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp) to know their specific use.

In general, a pre-harvest aid (glyphosate and Heat LQ) should be used to increase plant tissue drydown and kill green weeds. The correct stage is 60-75% seed colour change. Expect to harvest the crop 1-3 weeks after spraying, similar to the time expected between swathing and harvesting.

A desiccant with the active ingredient diquat works more quickly, forcing removal of crop moisture. A fast-acting product, expect to harvest 4-7 days after application. Target a minimum of 90% seed colour change, as diquat will lock in any remaining green chlorophyll in the seed.

Points to Consider

Caution is advised when swathing or desiccating a canola crop, since that is considered growth and development termination, according to pre-harvest interval (PHI) standards. Know the length in days PHI of the fungicide and/or insecticide used on the crop; swathing or desiccating should not take place before that PHI window closes.

More tips on canola harvest management can be found here: https://www.canolacouncil.org/media/530966/canola_swathing_guide.pdf

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It’s Probably Not Giant Hogweed – 2018

Because of our experience with crops and weeds, it’s no surprise that the general public often turns to agronomists for plant identification and management advice. And it’s usually about this time of year – when Ontario puts out giant hogweed advisories and big white umbels are in bloom across Manitoba – that these calls start to pour in.

Cow Parsnip

Fortunately, it’s probably not giant hogweed (Heracleum mantegazzianum) since that invasive species has yet to be found in our province.  It’s more likely another member of the carrot family – cow parsnip (Heracleum maximum).  Unlike its giant cousin, cow parsnip is native to Manitoba and non-invasive.  It’s also very attractive to pollinators.

But even though it’s probably not giant hogweed, it’s still best not to touch it. Because, much like its giant cousin, the sap of cow parsnip may cause dermatitis when in contact with exposed skin.  Symptoms include photosensitivity, a rash and/or blisters.  Reactions to cow parsnip sap are generally much less severe than those to giant hogweed sap.

For more information, see poster on Poisonous Plants in the Carrot Family on Manitoba Agriculture Weeds landing page

 

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Is it Time to Make Wheat Protein?

Wheat growers are nearing decision time on whether to supplement their wheat crop with nitrogen for protein enhancement.

Currently it is suggested that if the yield potential of the wheat crop looks good, and higher than for the N rate initially supplied (i.e. at 2 lb N soil and fertilizer per bu), consider trying a treatment. And check with your marketing consultant whether market signals suggest a shortage of high protein wheat being harvested elsewhere.

Full report and details on treatment and results from University of Manitoba study found on the Manitoba Wheat Barley Growers Association website: Time to Make Protein – The Wheat Grower’s Decision

 

 

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Are the conditions right for sclerotinia in canola?

There are a few points to remember when considering a fungicide application for sclerotinia in canola this year:

  • In order for sclerotia to germinate and produce apothecia, they require at least 10 days of moist soil conditions (surface soil – as we aren’t concerned with sclerotia that are buried more than an inch or two below the surface).
  • Spores cannot infect leaves and stems directly – they grow on senescing tissue (i.e. canola petals) and then spread to the leaves and stems.
  • Dew/rainfall after petal drop is required for the pathogen to spread from the infected petals to the stem. Petals that dry up in leaf and branch axils without any moisture will not spread the infection.
  • The recommended timing for a fungicide application for sclerotinia management in canola is 20-50% bloom. This is because typically the canopy has filled in after 50% bloom. Petals can still be infected after 50% bloom, but when they fall, they tend to land on upper branch axils. Infection that only affects minor upper branches will not have a large impact on yield. If a crop is stagey or the canopy thin, infected petals may land on lower leaf and branch axils even after 50% bloom and infect the main stem. As long is there are petals present on the plants there is potential for infection to occur, the question is where will those petals land when they fall?
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Corn Concerns & Curiosities

 A number of things are showing up in the corn patch, now that corn is actively growing and farmers/agronomists are scouting for emergence, growth and weeds.

  • Uneven emergence
  • Herbicide Injury
  • Scorthed Leaves
  • Wilted/Discoloured Corn
  • Sand-blasted Corn
  • Grey Corn Leaves
  • Yellow/Twited Corn Leaves

To see pictures and find out what is causing them see corn-concerns-curiosities (PDF 1.88MB)

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Hail Damage – What is the Yield Loss in Cereals & Corn?

Submitted by Anne Kirk, Cereal Crop Specialist, Manitoba Agriculture

Hail has been reported in several areas of Manitoba, and due to the size of the hail and duration of the storm, crops were affected in some areas.  Assessments of damage will occur over the next few days.  The amount of loss expected from a hail event depends on the severity of hail, crop type, and the growth stage of the crop.

Spring Wheat – is least susceptible to hail damage prior to stem elongation since the growing point is below the soil surface and will likely not be damaged.  Hail damage during jointing or in the boot stage is difficult to assess.  Spikes can still pollinate and fill, and regrowth from new tillers can occur.  The more advanced the wheat is at the time of hail the greater the yield loss.  The greatest yield reduction from hail occurs in the milk stage.

Oats and Barley –  will tiller and recover better from hail than wheat, especially prior to the boot stage.  Grower experience has demonstrated that barley hailed severely in the boot stage has recovered to produce 70-80% of normal yield.  Crop hailed prior to the boot stage should be left if stems or green tissue remains.

Corn – early season hail occurring when the growing point is still below the soil surface will result in very little yield loss.  At the 6 leaf stage the growing point is above ground, but leaf loss without damage to the growing point has a small impact on yield.  Yield loss as a result of hail can be estimated by determining percent leaf defoliation (Table 2).   Leaf area removed and leaf necrosis need to be considered, while damaged green leaf tissue should not be included.  Assess leaves 7-10 days after a hail event, so that living and dead tissue can be easily distinguished.

Assessing Damage – New growth should be evident within a few days after a hail event.  Assess crop to evaluate new crop growth.    Yield potential of a damaged crop will depend on rainfall and temperatures in the next 30 days after hail damage.

 

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Are You Staging Your Corn Correctly?

Submitted by Anne Kirk, Cereal Specialist, Manitoba Agriculture

For more information see Manitoba Corn Growers newsletter for Growth Stage Information for Herbicide Application

When applying post-emergent herbicides, proper corn growth staging is extremely important. Herbicide labels may refer to plant height, crop growth stage, or both when listing crop stage timing. Farmers and agronomists need to accurately stage corn plants to ensure that herbicides are being applied at the correct stage. Some common methods of determining corn growth stage are listed below.

Figure 1: Corn Staging Diagram

Figure 2: Live Plant Corn Staging

 

Corn Height Method  Measure from the soil surface to the highest point of the arch of the uppermost leaf whose tip is pointing down.  Don’t measure to the “highest point” on the plant, which is often the tip of the next emerging leaf above.  Refer to Figure 1/2 on how to correctly determine the height of a corn plant. Corn height varies due to growing and crop management conditions, and is not the most accurate way to stage corn.

Leaf Over Method Count the number of leaves, starting from the lowest (the coleoptile leaf with a rounded tip) to the last leaf that is arched over (tip pointing down). Younger leaves that are standing straight up are not counted.  In Figure 1/2, the corn plant would be at the 4 leaf stage using the leaf over method.

Leaf Tip Method – Count all leaves, including any leaf tips that have emerged from the whorl at the top of the plant. In Figure 1/2, the corn plant would be at the 6 leaf stage using the leaf tip method.

Leaf Collar Method (V-stage) –   Count the number of leaves with visible collars, starting from the lowest (the coleoptile leaf with a rounded tip) and ending with the uppermost leaf with a visible leaf collar. This method is the most common staging system and involves dividing the plant development into vegetative (V) and reproductive (R) stages.  The leaf collar method is generally also the easiest to use, and related better to the physiological stage of the plant and therefore to the effects of herbicides.  In Figure 1/2, the corn plant would be at 3 leaf stage (V3) using the leaf collar method.

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Copper Deficiency in Wheat – Symptoms and Cures

Submitted by John Heard, Soil Fertility Specialist, Manitoba Agriculture
Classic symtoms of copper deficiency on soils likely low in copper are:
·         twisted leaf tips 
·         sandy, low OM , high pH soil with known low copper levels 
Or could it just be environmental stress due to frost injury, lack of moisture and drying winds?
A tissue test is needed to confirm copper deficiency as the culprit. 
Studies in Manitoba compared three timings of foliar copper sprays on deficient spring wheat and showed that copper deficiencies and impact on yield can be severe or slight and can vary from year to year.
Timing and application method are important to regain yield! For more information and pictures on copper deficiency, see the full .pdf copy of Copper Deficiency in Wheat
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