What is the value of that corn stover?

With corn harvest nearing there may be some questions about harvesting corn stover for feeding beef cattle. There are some implications for the crop farmer with regard to nutrient removal, future nitrogen needs, organic matter and erosion control.

Grain yield is usually about 45-50% of the total dry matter yield of a corn field. It is estimated that a 140 bu/ac corn field leaves about 4 ton/ac of roughage (at 25-30% moisture).  Table 1 includes some nutrient content values from past Manitoba studies1 compared to those of the International Plant Nutrition Institute2.

Table 1. Crop nutrient removal with a 140-150 bu/ac corn crop.

  Stover amount Nitrogen (N) Phosphorus (P2O5) Potassium (K2O) Sulphur

(S)

    Lb nutrient/ton
IPNI average Per dry ton 19 5.7 32
MB Ag Per dry ton 12 4 34 1
    Lb nutrient /acre
All stover removed At 4 t/ac

(2.7 DM ton)

33 11 96 3
½ stover removed At 2 t/ac 17 5 48 2

 

What is the approximate value of fertilizer nutrients removed in stover?

Using the MB Ag values from table 1, the approximate value of nitrogen, phosphorus, potassium and sulphur per dry ton of harvested corn stover is $6, $2.40, $10.20 and $0.40, respectively (based on fertilizer prices of $0.50/lb N, $0.60/lb P2O5, $0.30/lb K2O and $0.40 /lb S) for a total nutrient value of $19/ton.  If harvested stover yields are 4 ton/ac (2.7 dry ton/ac), the total value of nutrients removed from the field would be $51.30/acre.  Since the full stover amount is seldom harvested, the removal would be reduced accordingly.  Note that over half the nutrient value removed is as potassium.

Implications:

One might conclude that all nutrients need to be replaced to sustain continued crop production. But this may not be the case:

  • clay textured soils in Manitoba tend to have high natural reserves of potassium.
  • Potassium is readily leached from mature crop residues, so rained on and delayed corn stover removal will leave much of the potassium in the field.
  • since stover harvest is done only occasionally, it will impact soil test levels slightly
  • nitrogen requirements may actually be less for the next crop (read on)

Nitrogen needs of the following crop may actually be reduced when some corn residue is removed. With the typically high residue loads of corn stover and the relatively high C:N ratio, inorganic soil N levels can be depressed during residue decomposition, called immobilization.  This temporary tie up of nitrogen by microbes to breakdown residue will be less if there is less stover. US studies with corn following corn have shown that optimum N rates may be 10-45 lb less N per acre when half the residue is removed.   We grow little corn following corn here so may not such large differences.

Now if corn stover was grazed by cattle, many of these fertilizer nutrients would simply remain in the field, but most crop farmers want cattle off the field so they can complete fall tillage operations to prepare for the 2019 crop season.

Erosion, organic matter levels and soil structure would be negatively affected by full and continuous removal of corn stover, but not likely by occasional removal. Mechanical harvesting (usually stover cutting with a rotary hay cutter, raking with a double rake, then baling) may only remove some 40% of the total stover biomass, generally leaving sufficient soil cover.  And since Manitoba corn stover is usually aggressively tilled, this reduced cover will require less than normal tillage to prepare a seedbed for springtime.

In summary, the occasional removal of a portion of the corn stover should have minimal effect on soil properties – other than nutrients. Soil testing is important to know if you have such nutrients to spare or how much to charge for such removal.

References:

1 Heard, J. 2004.  http://www.umanitoba.ca/faculties/afs/MAC_proceedings/proceedings/2004/heard_nutrient_uptake_corn.pdf

2Fixen, P. 2007. Better Crops/Vol 91, no.1) https://www.ipni.net/ppiweb/bcrops.nsf/$webindex/BD81AB2128ECC7D2852572DE005B4364/$file/07-2p12.pdf

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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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Scouting & Management of Sunflower Rust

Rust in sunflower is caused by the fungus Puccinia helianthi, which overwinters on plant stubble and produces five spore‐stages throughout the year. Early in the season, orange rust pustules appear on the upper surfaces of cotyledons of seedlings and volunteer plants, with later infections moving to the underside of the leaf (Figure 1).  The most yield-damaging stage occurs in late July to early August, when symptoms of infection show up as dusty, dark brown pustules on leaf surfaces, petioles and flower bracts (Figure 2). As the disease develops, black teliospores form, overwintering on the crop residue.

 

Figure 1: rust on leaf underside (photo: MB Ag)

 

Figure 2: Rust on leaves, stem. Wilting plants (photo: MB Ag)

Sunflower rust becomes a more severe issue in later-planted crops, or crops with weaker genetic resistance. Warm, moist weather favours rapid multiplication of rust spores, and windblown spores can travel quickly from field to field.  Early stages of sunflower rust in 2018 have been observed in the Cypress River area the week of July 3rd.

High plant populations and dense, leafy canopies allow humid conditions to remain in the crop throughout the day, compounding injury from rust spores.

Scout sunflower fields regularly to monitor the development and stage of rust infection. Watch for dense clusters of brown, powdery pustules scattered over all plant surfaces.  Orange-brown ‘dust’ on clothing after being in a sunflower field is a key indicator that rust is present, and more careful scouting is needed. Withered lower leaves are an indication that the surface is heavily infected.

Controlling rust after infection is primarily done using triazole-based and strobilurin-based fungicides. Recommended action in rust-infected crops is to use a fungicide from the triazole group after the first onset of symptoms, at the 2-3% pustule coverage on the upper four leaves at flowering (R5).  Strobilurin-based fungicides act more as a ‘protectant’, applied earlier before widespread infection occurs.

See more information on sunflower rust at https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp

See Guide to Field Crop Protection for more information on fungicides registered at https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp

National Sunflower Association of Canada information on Sunflower Diseases: http://www.canadasunflower.com/wp-content/uploads/2012/11/Disease.pdf

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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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