In agriculture, selection of the optimal planting date is one of the most critical factors in the decision-making process. When 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 March 6-13, average weekly soil temperatures at 4 inches varied greatly among crop reporting districts, overall varying from a decrease of 3 to an increase of 4 degrees F (Figure 1). For example, in the eastern region, soil temperatures decreased by 1-3 degrees F; while in the northwest region, soil temperatures increased by 2 to more than 4 degrees F.
Average weekly soil temperatures at 4 inches varied across Kansas, with temperatures below 40 degrees F in the northwest corner and close to 50 degrees F in the southern portion of the state (Figure 2). For example, in the northeast region, soil temperatures fluctuated between 40 to 44 degrees F.
Lack of precipitation across the state is also influencing the temperature fluctuations experienced in the last week. (Figure 3). Dry conditions will help the soil warm up but planting should be delayed until optimal soil moisture conditions are reached.
Each summer row crop has an optimal soil temperature for emergence. The minimum temperature for corn is 50 degrees F for germination and early growth. However, uniformity and synchrony in emergence is primarily achieved when soil temperatures are above 55 degrees F. Uneven soil temperatures around the seed zone can produce non-uniform crop germination and emergence. Lack of uniformity in emergence can greatly impact corn yield potential. This is particularly true for corn, since it is the earliest summer row crop planted. When soil temperatures remain at or below 50 degrees F after planting, the damage to germinating seed can be particularly severe. Corn is also more likely than other summer crops to be affected by a hard freeze after emergence if it is planted too early.
Producers should consider all these factors when deciding on the optimal planting time.
For more information about how we collect temperatures and how to use them, visit our Soil Temperature Explanation page at http://mesonet.k-state.edu/about/soiltemp/data/.
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Mary Knapp, Weather Data Library