Cold temperatures and injury to newly planted corn
Corn planting progress throughout Indiana in 2014 has been slow to date. As of April 27, USDA-NASS estimated that 8% of Indiana's corn crop had been planted, compared to an average of 26% for the past five years. The primary reasons for the slow start have been wet soil conditions and cool soil temperatures. Where soil moisture was acceptable for planting, some growers accepted (or ignored) the risks associated with cold soils and corn germination or initial seedling development and planted corn. Should they be concerned about the health of their newly planted and, in a few cases, newly emerged crops? Well, we'll know for certain come harvest time. But in the mean time, we can talk about possibilities.
Newly Planted Corn
One of the risks that newly planted corn faces is that of imbibitional chilling injury due to cold soil temperatures during the initial 24 to 36 hours after seeding when the kernels imbibe water and begin the germination process. In response to the imbibition of water, kernels naturally swell or expand. If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process. Some sources indicate that the injury is not so much due to literal cell membrane rupture, but rather to the failure of embryonic cell membranes to reorganize their structure from a dry and somewhat "leaky" state to a rehydrated and less permeable state during the initial period following imbibition. Regardless of the cause, the 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.
It is not clear how low soil temperatures need to be for imbibitional chilling or subsequent chilling injury to occur. Some sources simply implicate temperatures less than 50F (10C). Others suggest the threshold soil temperature is 41F (5C). Daily minimum soil temperatures at the 4-inch depth (typical depth for National Weather Service measurements) have been in the mid- to high 40's F around the state in the past week or so, especially in the northern third of the state. Elsewhere, daily minimum soil temperatures have ranged from the low 50's to the low 60's; probably warm enough NOT to cause imbibitional chilling injury to corn.
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.
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