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With this week’s forecasted low temperatures projected to dip into the high 30s (°F) with potential rain events, growers have asked if/how germination will be affected for corn and soybean planted this week.
Imbibitional (fast) water uptake occurs within the first 48 hours after a seed is planted. Once planted, corn seeds need a two-day (48-hour) window and soybeans need at least a 24-hour window when the soil temperature at planting depth does not drop much below 50°F.
When the soil temperature drops much lower than 50°F within that time frame, there is potential for chilling injury to affect seed germination and seedling growth. Soil temperature decreases after this time are less likely to affect seed germination.
Check the weather forecast and soil temperatures for your area. It’s also important to check the soil temperature of each field the morning you intend to plant. (This can be done with a meat thermometer.)
Second, check on your seed tag or with your seed dealer regarding the cold tolerance of your corn hybrids/soybean varieties. Hybrids and varieties vary in cold tolerance and company rating scales differ. However, be aware that imbibitional chilling is a physical phenomenon that can override genetics.
Cold Stress in Corn
When corn seeds imbibe (take up) water, cell membranes stretch and cells expand. When a damaged cell membrane rehydrates, it may not return to its normal shape and size. This can create a “leaky” cell. Water is at its densest at about 39°F so when cold water is imbibed, it may result in additional membrane damage.
These ruptured membranes may occur in the cell walls and in the mitochondria. In the plant this action may disrupt the embryo/endosperm enzymatic conversion to energy, but mostly results in leakage of cell solutes and sugars. This, in turn, is likely to reduce growth rate and interfere with growth of the emerging seedling.
Cold Stress in Soybean
Soybean germination consists first of a very fast uptake of water (imbibitional phase) followed by a much slower uptake of water (osmotic phase). Chilling during the first phase can cause severe problems because the imbibed water is needed to rehydrate the cotyledons and embryo to the point that cell membranes become functional. Cold temperatures interfere with proper hydration of those membranes.
During the second phase of germination, the fully functional membranes (after imbibitional hydration) create an osmotic situation in which water diffuses into the living cells. Osmotic water uptake is slow with cold temperatures. Chilling during this phase causes little direct injury to the germinating seedling. Cold temperatures will, however, slow emergence.
In conclusion, check the weather forecast, soil temperature, and hybrid/variety cold tolerance before planting. The first 24- and 48-hour periods are critical for soybean and corn, respectively, if soil temperatures dip much below 50°F. Monitor your fields based on planting date throughout the year to determine any effects on plant stand and yield.
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