Selection of the optimal planting date is one of the most critical factors in the decision-making process for producers. In making this decision, producers should consider soil temperatures rather than just calendar dates. After a very warm start to March, air temperatures across Kansas declined this past week.
For the week of April 10-16, the difference in maximum and minimum soil temperatures at 2- and 4-inch soil depths ranged from less than 10 to more than 40 degrees F (Figure 1). For example, in the northeast region, soil temperatures varied close to 30 degrees F; while in the southwest region, soil temperatures varied from 20 to more than 40 degrees F at the 2-inch soil depth (Figure 1; upper panel). Soil temperature variations for northwest and southeast areas of Kansas ranged from 20 to 30 degrees F (Figure 1; upper panel). Lower ranges of soil temperature fluctuations were experienced at the 4-inch soil depth, but were still from less than 10 to more than 30 degrees F (Figure 1; lower panel). The largest variation was observed in the south central part of the state (> 30 degrees F); while the lowest variation was recorded in small pockets within the northwest and southeast regions (<15 degrees F).
Daily soil temperature variation within the last week (7-day report) was recorded across Kansas for several locations (Figure 2), presenting variations around 20 degrees F. Soil temperatures were above 60 degrees F for Friday April 13 in several locations, suddenly dropping to at or less than 40 degrees F on Monday, April 16 (Figure 2).
As published in the eUpdate on April 13, 2018, cold temperatures can result in injury to the germinating seed as it is absorbing moisture – a problem called imbibitional chilling injury. When soil temperatures remain at or below 50 degrees F after planting, damage to germinating seed can occur.
Soil temperatures at the 4-inch depth during the first 24-72 hours after planting, when the kernels imbibe water and begin the germination process, are critical. Kernels naturally swell when hydrating (taking in water). If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process, resulting in “leaky” cells. Injury symptoms may include swollen kernels that fail to germinate or aborted growth of the radicle and/or coleoptile after germination has begun.
Chilling injury can also occur following germination as the seedlings enter the emergence process, reducing plant metabolism and vigor, potentially causing stunting or death of the seminal roots, deformed elongation (“corkscrewing”) of the mesocotyl, leaf burn, and either delayed or complete failure of emergence, often leafing out underground. Chilled seedlings may also be more sensitive to herbicides and seedling blights.
Before making any decisions, fields should be scouted 4-7 days after the cold weather occurred since the extent of the damage and potential for new growth will be evident during this time.
Producers should consider all these factors when deciding on the planting time. More information about the planting status of summer row crops will be provided in upcoming issues of the Agronomy eUpdate. Stay tuned!
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Mary Knapp, Weather Data Library