Crop Germination – What Soil Temperatures are Needed?

Soil temperature drives germination and seedling emergence, so how cold is too cold?  What is your soil temperature at your targeted seeding depth….today? Finally, when should you be measuring the soil temperature?

The following are the minimum temperatures needed for germination to begin in various crops.  These values should be regarded as approximate, since germination depends on factors other than just temperature.  But, if soils are too cool, germination will be delayed and cause uneven or poor seedling emergence.

 

Crop Temperature     (°C)
Wheat 4
Barley 3
Oats 5
Corn 10
Canola 5
Flax 9
Sunflower 6
Edible Beans 10
Peas 4
Soybeans 10

Sources: North Dakota State University Extension Service, Alberta Agriculture & Rural Development and Canola Council of Canada

Getting an accurate measure on soil temperature

Determine how deep you will be seeding. Then place your soil thermometer at the targeted depth. Take two measurements throughout the day: one in the morning (8am) and one in the early evening (8pm).  Average the two readings to determine the average soil temperature. The recommendation is to take readings for two to three days to establish a multiple day average and to measure at a number of locations in the field, to account for field variability.

Still not sure and short on time?  See the soil temperature data for various locations across Manitoba from the MB Ag-Weather Program: https://www.gov.mb.ca/agriculture/weather/soil-temperature.html.  This can be used as a guideline for an area, but in-field measurements are going to tell you what is actually going on in your field!

 

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Can recent cold temperatures & snow impact corn emergence?

Cold temperatures, combined with excessive rainfall in some areas and even snowfall, has created conditions not ideal for the germination and emergence of corn planted recently in Manitoba. Research has shown that temperatures at or below 10°C are most damaging to the germination and emergence process, especially if the cold temperatures persist long after planting.

What is Imbibitional Chilling Injury? Firstly, imbibition is the process by which seeds absorb water for the initiation of germination. In corn, kernels must absorb (imbibe) about 30 % of their weight in water before germination begins (by comparison, soybeans must imbibe about 50 % of their weight in water).

Imbibitional chilling injury may result when water colder than 10°C is imbibed, and effects can be particularly severe in situations where seeds were planted into cool soils (10°C or colder), combined with cold rain or melting snow after planting (the most critical time for imbibition is within 24 hours of planting). The absorption of cold water can disrupt the reorganization of cells during rehydration and can result in the loss of seed vigor or seed death.  Note: A cold, heavy rain after planting seems to increase the chances of imbibitional injury, probably because it overwhelms the ability of the soil to warm the water before it reaches the seed (Source: Joel Ransom, NDSU). 

Symptoms of imbibitional chilling injury include swollen kernels that swell but fail to exhibit further signs of germination or arrested growth of the radicle root and/or coleoptile following the initiation of the germination process.

Instances of non-imbibitional chilling injury following germination during the emergence process can also occur, often causing stunting or death of the seminal root system, deformed elongation of the mesocotyl (the so-called “corkscrew” symptom) and either delayed emergence or complete failure of emergence (i.e., leafing out underground). This type of chilling injury is more closely related to physical damage to the outer cell tissues that literally cause death of the plant part or inhibit further elongation of the affected area. Thus, chilling injury to only part of the circumference of the mesocotyl results in the “corkscrew” symptom as the undamaged sections of the mesocotyl continue to elongate.

The Result of Cold Injury? If germination is impacted, poor stands could result impacting yield potential.  Plants that also develop from injured seedlings may be stunted and develop more slowly than normal plants.  This can result in unevenness in the growth stages of plants within the field.

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD 

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Did my early seeded wheat survive this latest cold snap?

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

In my position, I talk with with numerous agronomists (both public & private) regarding cereal crop production.  Often issues facing Manitoba producers are issues facing producers to the east, west and south of us.

One such instance is Jochum Wiersma, who is the Cereal Specialist with the University of Minnesota, recently wrote an article on what the latest cold snap may have had on the earlier planted cereal crops in his area.  However, the information is truly applicable to conditions facing some acres here in Manitoba. Below is the article, along with the link to his blog post.

Did my earliest seeded wheat, barley, and oats survive this latest cold snap?

by Jochum Wiersma

The latest cold snap may have you wonder whether the earlier planted wheat and barley have a snowball’s chance in hell to produce a healthy seedling and stand?  Wheat, barley and oats do not germinate until the soil temperatures reach 40 F (4.4C).  The germination process starts with the uptake of water, breaking the dormancy and starting the development of the sprout.  Once the dormancy is broken the energy stored in the seed is used for the growth and development as well as respiration (basically maintenance).  If the temperatures are low or even freezing the growth and development of young seedling slows down or even stops.  However, respiration continues albeit at a lower rate and continues to deplete the energy stored in the seed.  This will eventually decrease the vigor of the seed and may prevent the sprouted seed to produce a healthy seedling.

With the freezing temperatures the first concerns is whether this can kill the sprouted seed.  Reports from the literature indicate that sprouted wheat and young seedling will likely survive temperatures in the low twenties (20F = -6.7C).  A quick first check of the color of radicle (first root) and coleoptile (first leaf) is the first step: a white and firm radicle and coleoptile will indicate that the sprout is not damaged by frost after the seed has been allowed to thaw out. A second test to determine viability of seed is to dig up seed and bring it home, place it between moist paper towels, and keep it at room temperature.  If the seed is viable the sprouts should start to grow within 24 hours.

Minnesota Crop News: http://blog-crop-news.extension.umn.edu/

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Weathering & Seed Quality

Securing seed supply requires farmers to be informed to make good decisions and to manage potential risks. As an old saying goes “Quality in equals quality out”, so farmers must place emphasis on planting high quality seed.  Regardless of seed source, it is recommended that growers obtain as much information as possible on the seed lot in order to make informed decisions. It only makes sense as there is only one opportunity to set the crop up for success.

In 2014, poor harvest conditions led to downgrading of cereal grains due to weathering factors such as sprouting and mildew. Questions in regards to the potential of downgraded wheat for seed supplies has been raised.  First, what is sprout damage and mildew?

Sprout Damage.  Sprout damage is pre-harvest germination. Germination begins when mature kernels absorb water and generate enzymes that break down stored starch and protein in the endosperm. The enzymes release sugars from starch and amino acids from proteins which nourish the growing embryo.  One of these enzymes is called alpha-amylase which is the enzyme measured when conducting the Falling Number test.   Keep in mind though you don’t need to see a visibly sprouted seed for those germination processes to have started within the seed.

Mildew.  Mildew is indicated by grey discolouration on the brush or distal end of the kernel.  Mildew is associated with weathering and sprout damage. It is saprophytic or non-pathogenic.

So if you have weathered seed and are wondering if you should use this seed for replanting next year, some tips are:

  • Although visual assessments can be a good starting place in selecting quality seed, testing is critical since it is the most accurate way to determine the ability of seed to germinate, and additionally the presence of disease and vigour.  A grade and protein assessment at the elevator or by the Canadian Grain Commission is not a verification of seed quality for planting.
  • Have tests conducted at an accredited lab. Home germination tests do not count!  Take a representative sample, after cleaning the seed lot.  It would be a good idea to phone the accredited lab you are submitting samples to so you can follow their procedures for sampling and submitting.
  • Have samples tested as early as possible so you know what you are working with.
  • However, if you do test early and results come back positive that the seed lot would be suitable for seed, I would encourage re-testing in early March. Germination can decrease in the bin over the winter, especially if the seed was immature, sprouted or otherwise damaged at harvest.  Therefore, it would be a good investment to test again in early March – that would allow you to have results back by late March, still giving you time to react and source new seed if the tests come back not as positive.

Finally, remember that best seeding practices — adequate seed bed preparation, proper seeding depth, using a seeding rate based on germination and thousand kernel weight to achieve your target plant stand, and use of seed treatments if necessary — will not rescue a poor seed lot!

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

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