Maize for Grain
SOIL TEMPERATURE AND MAIZE EMERGENCEBack to Technical Insights
• Maize is a warm season crop. Germination is optimum when the soil temperature is 10˚C and rising. Cool conditions during planting impose significant stress on maize emergence and seedling health.
• Maize seed is particularly susceptible to cold stress during and immediately after imbibition. Cork-screw mesocotyl is a common symptom of cold stress during the germination process.
• Lighter textured soils are more vulnerable because the night-time temperatures can drop below 10˚C inflicting stress on maize emergence.
• If stand establishment has been compromised by low soil temperature, assess the degree of damage and if necessary, plan to replant as soon as possible.
Maize is a warm-season crop which establishes and performs best when soil temperatures are warm. Soil temperatures at planting are a key environmental component of good stand establishment. It is generally recommended that growers’ plant when the soil temperature is 10˚C and rising. Warmer soil temperatures after planting are also critical for even stand emergence.
MAIZE SEED GERMINATION
The early stages of imbibition or water uptake into a dry seed represent a crucial period for seed germination (McDonald, 1994). Once a maize seed absorbs around 30% of its weight in water the seed is committed to the germination process and it cannot turn back. When seed that has absorbed water experiences cool temperatures for an extended time imbibitional chilling may occur. Delicate shoot cell membranes rupture in cold soils. Resultant seedlings may either "corkscrew" (see Figures 1 and 2) or completely fail to emerge as a result. This may also happen when there are rapid changes in air temperatures. (Elmore, 2012).
Figures 1 and 2. Imbibitional chilling (Elmore, 2012)
The mesocotyl is the white, tubular, stem-like part of the plant which is located between the kernel and the base of the coleoptile (Figure 3). As the coleoptile nears the soil surface, light causes a change in the supply of one or more growth hormones from the coleoptile to the mesocotyl tissue and mesocotyl elongation comes to a halt (Vanderhoef & Briggs, 1978). If mesocotyl elongation and/or coleoptile emergence are compromised, the emergence of leaves from the coleoptile may occur beneath the soil surface and be trapped by the soil (Nielsen, 2015). Little, if any mesocotyl or coleoptile growth occurs in soils cooler than 15˚C (Elmore, 2011).
Figure 3: Maize seedling development
Chilling injury following germination results in 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 (Manitoba Corn Growers, 2017).
Seedlings adversely affected by wide swings in soil temperature will have stunted and distorted leaves and may or may not emerge from the soil (Iowa State University, 2018). Stand emergence can be erratic with crop development varying by up to two growth stages.
Cold soils and/or wide fluctuations in soil temperatures throughout the day during the emergence process are thought to be major contributing factors for corkscrew mesocotyl development.
Figures 4-6: Corkscrewed mesocotyls
Corkscrewed mesocotyls can also occur when the coleoptile encounters resistance as the mesocotyl elongates. Severe soil crusting or otherwise dense soil surface and cloddy soil surfaces can cause such resistance. Certain herbicides, notably cell growth inhibitors like acetochlor, can affect seedling development especially if weather or soil conditions are not conducive for rapid seedling growth. Often more than one causal factor exists in a field and they usually interact with each other to amplify the problem (Nielsen, 2015).
IMPACT OF SOIL TYPE
Growers are often able to plant fields with sandier soils earlier in the spring because they dry out faster than heavier soils. However reduced stands after early planting have often been noted in sandier soils. Sandy soils have lower water holding capacity than heavier soils. As such they tend to experience wider fluctuations in temperature especially on clear nights with cold air temperatures (Stoll & Saab, 2013).
In 2009, soil temperatures were recorded at a 5cm depth in sandy soils in Wisconsin. Daytime soil temperatures reached acceptable levels for maize development (over 10˚C) for the first week however early morning temperatures dipped as low as 2˚C and the temperature difference between 6am and 6pm was close to 10˚C. An average 25% stand loss was observed at this location suggesting day-night temperature fluctuation after planting can pose an added stress on germinating maize (Stoll & Staab, 2013).
Figure 7: Soil temperatures at 6am and 6pm for seven days after planting in a stress emergence field in Wisconsin in 2009 (Stoll & Staab, 2013).
TIPS TO HELP MITIGATE EARLY-SEASON STRESS EFFECTS ON EMERGENCE
Planting date is one of the most important factors in stand establishment. The likelihood of reduced stands is greater when planting into cold soils or directly before when cold, wet weather is expected. To help mitigate risk consider the following tips:
- If a cold, spell is expected around planting time, stop planting 1-2 days in advance.
- In lighter soils, be aware that low night-time temperatures can dip soil temperatures below advisable planting levels. Large temperature swings can hurt emergence.
- Delayed emergence during cool conditions lengthens the duration which seedlings are most vulnerable to early season insects and diseases. The right seed treatment can help minimise further seedling losses from these factors.
New Zealand’s variable island climate means bad weather is often hard to predict. If you have experienced maize germination issues for any reason, you need to work quickly to determine whether the plant loss justifies a replant and if so, get some more seed in the ground as soon as possible. Your local Pioneer Area Manager can help determine if you should replant some or all your crop.
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Revised: November 2018
Expires: November 2020