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Spring warm-up: How does 2018 soil temperature compare?

The calendar says it’s time for spring field activity in Ohio and farmers are eager to prep fields and plant this year’s crops. However, average temperatures across Ohio have remained cooler than usual with the previous 30-day period (March 16 – April 15, 2018) running 2 to 6 degrees Fahrenheit below normal (based on 1981-2010). Combined with precipitation up to twice the normal amount in some areas, the weather is certainly not cooperating with ideas of an early jump on planting.

Late last week, Ohio experienced a strong warm up in air temperatures, which definitely warmed the first few inches of the soil surface (see “OARDC Branch Station Two Inch Soil Temperatures by Greg LaBarge). But how do the present conditions compare with the long-term mean? Figure 1 shows two-inch soil temperatures (Fahrenheit) for selected OARDC Weather System (http://www.oardc.ohio-state.edu/weather1/) stations from around Ohio. These soil temperatures are based on the weekly average for April 9-15, 2018. In addition, a long-term mean for the same 7-day period for 2000-2017 was calculated, and the differences between 2018 and the long-term mean are also displayed for each station.

Figure 1 is predictably showing the coolest soil temperatures across northern Ohio with the warmest soil temperatures just above 50 degrees Fahrenheit for the southern stations at Piketon and Jackson. Of course, soil temperatures can vary considerably based on soil type (e.g., sandy vs. clay) and other factors. Compared to the long-term mean (2000-2017), both two-inch and four-inch (not included in Fig. 1) soil temperatures are running 2-7 degrees colder than the long-term mean. In fact, for all stations analyzed, 2018 ranks within the top 5 coldest average 2” soil temperatures for this same period in April. This is consistent with the cooler-than-normal air temperatures that have recently impacted Ohio.

Making the decision to plant into cold soils can increase the risk of slow emergence and uneven stands, since both corn and soybean seeds germinate more slowly in cooler soils. Corn seedling injury due to imbibitional chilling may occur when soil temperatures fall below 50 degrees F. For this reason, it is important to look at the next 24-36 hours to determine the risk of soil temperatures dropping below that threshold. Soybean seeds absorb water more quickly than corn and as a result the risk of injury is greatest close to planting. Because of this, the 24 hours following planting are critical.

Soil temperatures are an important variable that you should consider to when making the decision to head to the field. With all the pressure to get started planting, it is important to take the time to be sure you are setting your 2018 crop up for success.

Figure 1. Average soil temperatures at 2” for April 9-15, 2018 and differences compared to a long-term (2000-2017) mean for selected OARDC Weather System stations. Each station’s 2018 ranking compared to the full period is included inside the star location icon.

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