SPRING has sprung and the calendar has hit April. Although, most farmers across the Prairies have started seeding some cereals and other crops, it is important we keep our corn in the bag! We can not let the calendar, or the neighbour, dictate when we should hit the field. Our best indicator to start planting corn is soil temperature and soil conditions. If we start planting into fields early when soils are cool and wet, we can expose that corn crop to stress. The single most important thing we can do right now is keep the seed in the bag and wait for warm soils.
‘Cold Stress’ - What is Imbibitional Chilling?
"Imbibition" refers to the initial uptake of water by seed during the first 24 to 48 hours after being planted into moist soil. The resulting rehydration causes the seed to swell and the germination process to begin. Imbibition occurs naturally, with no physiological processes involved (e.g. dry wood will imbibe water). This process occurs whether soils are cold or warm and for this reason there is the potential for "imbibitional chilling" injury on early planted corn.
The seed swells as it rehydrates, and this process damages the internal cell membrane structure. When seeds (and soil) are warm, the membrane damage is quickly repaired by the physiological activity associated with germination and "life goes on" normally. When seeds (and soil) are cold, their cell membranes are less elastic, resulting in cell membrane damage due to swelling – this is more severe and the physiological repair of the damage is slowed or stopped. Left unrepaired, this damage to cell membranes and the subsequent leakage of cell contents can result in death of the seed. By understanding this process, we need to be certain that the seedlings first exposure to the soil and moisture needs to be warm (approx. 10°C). We know that the first 24 to 48 hours are crucial for germination and emergence.
Factors Influencing the Risk of Imbibitional Chilling Injury
Intensity and Duration of Cold Soils
Obviously, 5°C soil temperatures represent a higher risk than 10°C temperatures. A single day of cold soils is likely less risky than multiple, consecutive days of cold soils.
Daily soil temperature fluctuation is more dramatic in dry soils than in moist soils. That means higher daily maximums and lower daily minimums.
Plant Residue Cover
Daily soil temperatures fluctuate less in no-till fields that have a lot of surface residue from previous crops or current cover crops. In particular, soil temperatures in such fields will not drop as rapidly or dramatically in response to a cold snap as will bare fields. That's the good news. The bad news is that soil temperatures in fields with heavy surface residues are generally lower to begin with than bare soils early in the season and so early planting of corn in no-till fields is somewhat riskier in general.
The Impact it Has on a Corn Crop
What happens: Corkscrewed
Its impact: Delays uniform
What happens: Poor root system
Its impact: Poor root development
What happens: Internal cell wall
Its impact: The cell wall leaks
You may not think having corn seed planted in cold soils will impact its growth until it rains; this is false. If there is any moisture present in the soil that the seedling can imbibe, then it is at risk. If soil temperatures are below 8°C then corn should be left in the bag.