By Mohammad Shamim
The relatively dry conditions in March this year provided an extended window of opportunity for growers to plant corn and soybean. As a result, most growers had completed planting by mid-April. However, early planting, typically favored for its high yield potential, came with two major challenges.
One key concern, likely resolved by the time you read this, was whether the seeds had lost their ability to germinate. Due to the lack of rainfall, soils remained dry, delaying emergence as seeds lacked sufficient moisture to imbibe (absorb water) and initiate germination. This concern arose because some growers hesitated to plant soybeans deeper, fearing that subsequent rainfall could create crusted or muddy soil conditions that would hinder seedling emergence. In addition, uneven emergence across fields led to speculation among some growers that germination itself might be compromised.
To investigate this, I collected soybean seeds that had remained in the field for approximately two weeks and tested their viability using a paper towel germination method. Within just two days, over 85% of these seeds germinated (though this does not directly reflect field emergence). This result suggests that the uneven emergence observed in the field was more likely due to planting depth and/or soil moisture conditions, and that seed remained viable despite a long rest in the soils.
The second major concern, which has become more apparent recently, is the impact of freezing temperatures on germinating soybean seeds and young seedlings. Recent rainfalls have come with some chilly weather. Low temperature is one of the most important factors limiting soybean productivity. Soybeans planted after mid-April often remained in the soil without emerging or emerged very slowly following rainfall events, leaving newly germinated seeds and seedlings exposed to cold stress.
When temperatures decline gradually, plants can sometimes adjust and partially acclimate to freezing and dehydration stress. However, soybean is a warm-season crop, and spring frost events are often sudden, giving plants little or no time to adapt. As a result, these conditions can quickly lead to injury or plant death.
Research has shown that short periods of cold exposure during the imbibition stage (when seeds first absorb water) usually have limited effects on soybean germination, with germination rates remaining above 85% after 10 days of exposure. In more detailed studies comparing temperature and soil moisture conditions, cooler day/night temperatures (around 50/50°F) still allowed germination above 60%, although emergence was delayed by four weeks. That said, the germination was still lower by 38% compared to 68/57°F with normal soil moisture.
However, problems become more severe when day/night fluctuations (around 68/57°F) occur together with excessive soil moisture. Under these conditions, germination can drop by 80%. In spring, cold conditions are often accompanied by rainfall, making excess moisture a common co-stress factor. In such situations, soybean emergence can be affected considerably, and the seedlings would die. The recent extended cold spells appear to have gone beyond these typical stress conditions and have resulted in visible frost injury in newly emerged seedlings. That said, the pattern and severity of injury appear to be limited to certain areas of the state. While scouting fields across several counties in western Kentucky, I observed symptoms of cold stress in soybean plants. Although this type of stress differs from permanent frost injury and will likely slow early growth, many plants are expected to recover once temperatures return to normal growing conditions.
Source : uky.edu