Plant According to Soil Temperatures

After a long winter and the arrival of spring, many growers are eager to get into the field. However, planting too early can have a negative impact on yield. It is important to plant according to soil temperature and conditions and be aware of potential issues caused by cold, wet soils.

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Corn requires a soil temperature of 50° F to germinate and grow. Temperatures below the optimum can cause seeds to sit dormant and become more vulnerable to diseases, insects, and animal predators. Planting into cold and/or wet soils can lead to numerous problems. When rain is forecasted, it can be tempting to put a rush on corn planting to avoid being delayed into the season. However, it may be better to wait if the forecast includes cold temperatures and precipitation. This is due to the physiological processes occurring in the first 24 to 48 hours after seed placement.

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Many corn growers believe that cold temperature damage is not an issue because the growing point of corn is at or below the soil surface until the V6 growth stage. This rule of thumb is usually the case regarding air temperature, but not always true with respect to soil temperature. In fact, wet soils with a temperature below 50° F may cause chilling injury during germination. Although it is possible to see this injury in corn, it is highly unlikely in good quality corn seed lots. Imbibitional chilling injury happens when a dry corn seed takes in cold water from rain or melting snow. Corn kernels imbibe 30% of their weight in moisture before germination can begin.1 Imbibition of moisture begins within the first 24 to 48 hours after planting.2 However, cold water can cause cell membranes to become rigid and rupture which may result in aborted radicles, proliferation of seminal roots, and delayed seedling growth. Such damage may limit or cease nutrient uptake, restricting normal development of the mesocotyl and coleoptiles, as well as allow for soil disease and pest entry.

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It is important to understand that symptoms of chilling injury can also be caused by other factors and may be compounded by additional stresses during germination, which include herbicide injury, disease, or soil crusting.

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Figure 1

Figure 1. Chilling injury to a corn kernel.

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A few typical symptoms may be:

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  • Seeds that swell but do not germinate.
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  • Deformed growth of the mesocotyl; corkscrewing (Figure 1).
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  • Visibly damaged areas of the mesocotyl or coleoptile.
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  • Fragile or absent primary root, mesocotyl, or coleoptiles.
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The diagnosis can be confused when looking at a combination of symptoms from a combination of causes. It is a good idea to evaluate fields largely affected by imbibitional chilling symptoms. If coleoptile and mesocotyls are missing or broken off, damage is fatal. Seedlings with coleoptiles and mesocotyls intact may have new leaf development and normal growth resume when temperatures warm and fields dry.