Potential Pitfalls of Planting in Cold and Wet Conditions

During our careers as farmers or agronomists, we’ve all experienced moments when the weather forecast suddenly shifts—from warm, dry, and sunny to cool, cloudy, and wet—right in the middle of planting. The problem with cold, wet weather is that it increases the probability of imbibitional chilling injury or cold shock syndrome. The key words chilling injury or cold shock truly describe what takes place to the seed.

When a plant starts its germination process, it takes in or imbibes (absorbs) water to rehydrate the cells causing the seed to swell. In corn, the seed must take in 30% of its weight in water to start the germination process. In soybeans, the seed must take in around 50% of its weight in water to germinate.

The first water that seeds imbibe usually occurs within the first 24 to 48 hours. If that water is cold (less than 39°F with corn and 45°F with soybeans), it may cause cells to burst or “leak”. This disruption of cells in a corn seed may cause the radicle to abort. It may also cause proliferation of seminal root development, corkscrewing of the coleoptile as it leaves the seed, as well as leafing out underground. In soybeans it may cause the seed itself to swell but the radicle will not fully develop, or the initial shock may cause the seed not to germinate. Seed coat thickness and or intactness can have an impact on how quickly water enters the seed and therefore the speed of absorption.

A seed or seedling that has cold shock syndrome takes more time to germinate and has a higher potential for disease to infect the seed or young seedling. Quality seed treatments can help protect the plant from disease, but they cannot protect the plant from cold water. Combine cold shock and disease, with other factors such as soil crusting, compacted soils, or deep seed placement, and you increase the likelihood of seed or seedling loss exponentially.

Another factor that may increase the severity of cold shock syndrome is the actual size/shape and or weight of the seed. It stands to reason that if you have a seed that weighs more you will need to bring in more water to reach your 30 or 50% of weight. If that water is cold, you also increase the potential for injury. Large rounds in corn tend to have more of an issue or concern when dealing with cold shock, either due to their weight, location on the cob during harvest, thickness of the pericarp, and/or how that seed dries.

Instances of cold injury in dry soil are also very common. When temperatures drop (28°F or less) the cold penetrates the top 1-3” of soil and kills plant tissue, the radicle and growing point.

The take home statement is that the first 24-48 hours of a seed’s life in the soil is critical to the health of the plant, how many plants you potentially could have at harvest, and subsequently yield.