Precipitation and cold temperature fluctuations within the first 48 hours after planting corn or soybeans can severely damage germinating seed and seedlings.
- Soil temperatures should be near 50° F and area weather forecasted to continue warming to ensure optimum growth and development after planting.
- Common damage symptoms such as “corkscrewing” and premature leafing are the result of damaged outer cell layers of the mesocotyl (first internode of the stem).
- Wait 3-5 days after better weather appears to accurately assess the viability of remaining plants.
Setting crops up for success means planting when soil and environmental conditions are best, but planting early to maximize the length of the growing season is equally important to many producers. Limitations of planting capacity (acres per day) and the number of days suitable for field work in the spring can result in disregarding unfavorable weather forecasts to allow planting additional acres before the next storm.
Figure 1 demonstrates a rapid drop in soil temperatures across a large geography following a cold front that occurred April 7 through April 14, 2020. Soil temperatures were adequate for planting (≥ 50° F) prior to April 7, but they dropped rapidly in the days following, potentially impacting seed germination and emergence. For example, soil temperatures reached 75° F near Salina, KS, on April 7, but were at or near 40° F by April 14 and remained below 50° F for several days. There are risks associated with wet, cold soils within the first 48 hours after planting.
Normal Germination Process
The germination process is driven by soil temperature as much as it is by moisture. Under favorable moisture and temperature conditions, with good seed-to-soil contact, the planting-to-emergence process will take as few as 6 days for corn (Graph 1), but it can take up to 5 weeks if soil temperatures drop below 50° F (data not shown). Soil temperatures of 50° F and above are needed to start inducing cell division and elongation and consistent, warm soil temperatures help increase the rate of germination. Soil temperatures lower than 50° F can be detrimental if occurring within the first 48 hours after planting.
Imbibitional Chilling Injury
Germination starts as soon as the seed begins to imbibe (absorb) water. A corn kernel will absorb about 30% and soybeans 50% of their seed weight in water, mostly within the first 24-48 hours after planting. This rapid uptake of water rehydrates the embryo of the seed, bringing the seed to life and starting germination.
Starch stored within the seed is the primary source of energy until roots begin establishing and leaves emerge from the soil to produce additional energy through photosynthesis. Seeds being rehydrated with cold rain or melting snow can result in damage to cell membranes known as imbibitional chilling. Hydration with chilled water can result in ruptured cells and cause swollen kernels, aborted radical development, terminated coleoptile growth and death of the seed. Symptoms of imbibitional chilling injury can appear as prematurely emerging leaves or swollen seed that never germinated. Injury will not always occur when soil temperatures are lower than 50° F, but it will be more visible as temperatures near 40° F and cold rain or snow events occur within 24-48 hours of planting.
Preemergence Freezing Damage
Cold temperatures can also impact successfully germinated seeds prior to emerging from the soil. Injury at this timing usually damages the outer cell layers of the mesocotyl causing premature leafing out of the plant. Curved mesocotyl and coleoptile (the protective sheath) symptoms, commonly referred to as “corkscrew”, can also be observed as a result of fluctuating soil temperatures, indicating the plant started and stopped growth to the soil surface. Cooler temperatures also slow the growth rate of seedlings, further exposing damaged plant tissue to injury from disease infections and insects.
Soil moisture levels and texture can also play a role in seedling damage due to their role in crusting of the soil surface that makes emergence more difficult. Finer textured soils with adequate soil moisture can help buffer soil temperature against fluctuating air temperature and better protect seed and seedlings. Drier, more coarsely textured soils will have less capacity to buffer against temperature swings, resulting in increased susceptibility of the seed and seedling to cold injury. Risk of damage from freezing temperatures increases as seedlings emerge and start to add leaves. After emergence, the plant growing point moves closer to the soil surface with each leaf that is added, further increasing its susceptibility to late spring frost occurrences.
Determining Extent of Damage
To determine the extent of damage from cold weather, it is important to wait 3-5 days after the weather has improved and growing conditions are favorable. This allows viable plants to develop once temperatures warm up and give a better indication of what stands will be like. Healthy emerging plants will have white to bright yellow stems and cotyledons that will quickly show new green growth. Seeds that are mushy and have a foul odor are not viable. Seedlings that are discolored and stunted are less likely to survive and produce normal yields.
Reducing Risk of Imbibitional Chilling Stress
In 2019, Golden Harvest® introduced a novel approach to seed vigor testing designed to better mimic imbibitional chilling stress that seeds face in less-than-ideal field situations. The new test was validated in actual field emergence trials, and in comparison with internal and external vigor tests prior to implementation. In addition to planting the highest quality seed, consider delaying planting until you are confident soil temperatures will be close to or above 50° F for the first 48 hours after planting.
For more information on potential chilling injury to corn and soybean, contact your local Golden Harvest Seed Advisor.
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