The importance of soil temperatures can be seen on many levels. The temperature of the soil controls seed germination, as the soil temperatures must be at an optimum level for a specific crop to grow strong seedlings.
Oklahoma's narrow planting window
In Oklahoma, there is a narrow window for spring-planted crops according to Ron Hays of Radio Oklahoma Network, publishers of the Oklahoma Farm and Ranch News daily e-mail update. Generally, Oklahoma farmers first plant corn which can take cooler soil temperatures. A little later in the season, when soil temperatures get up to the upper 60s to low 70s, farmers sow crops like cotton and soy beans.
"Farmers look at soil temperatures because they want to get crops planted as soon as they can, especially in a marginal state like Oklahoma," Hays said. "Other parts of the country have a window that's a little more forgiving, but it gets so hot here that if you don't have good growth on plants by the time you hit July and August, you're going to have a pretty hard time."
Planting 'ugly soybeans'
Farmers rely on soil temperatures as they try to plant spring crops as early as is safely possible. The crops' early growth may be stunted somewhat, but the plants recover later in the season.
"With soy beans, the recommendation is to wait for a little bit warmer soil temperatures, but farmers here go to the lower end of the range and plant when it's a little bit too cool," said Hays. "It's called 'planting ugly soybeans' because the plants look pretty anemic early on, kind of stunted. They come out of it, and it gives them a head start instead of waiting til you're in the optimal range of the planting window."
Hot soil means dry soil
The biggest crop for Oklahoma is wheat, and it is planted in early fall, Hays said. Farmers must then watch soil temperatures to avoid the hottest temperatures.
"We mainly plant wheat starting a week before Labor Day into October and the first of November," he said. "Both dryness and high temperatures can have an impact there. You've got to have some moisture, and you don't want 90s with no moisture to just cook the seed."
Temperatures then make a big difference in the quality and quantity of the grain produced, he said.
You also hear the soil temperature mentioned often during winter months, especially around the time of the first freeze of the season. When air temperatures are cold enough for frozen precipitation, the soil temperature is a good indication of whether or not the precipitation will stick to the ground.
The temperature of the soil fluctuates both daily and annually and those changes are most evident at or near the surface where sunlight has the most influence. A good place to find soil temperature data is what most meteorologists affectionately call "The Mesonet." The Oklahoma Mesonet is a world-class network of environmental monitoring stations. It consists of over 110 automated stations, and at least one is in each of Oklahoma's 77 counties. The Oklahoma Mesonet was designed and implemented by scientists at the University of Oklahoma and at Oklahoma State University.
"Your standard soil tempature graphic is the one that's 4-inches down," Hays said. "They also give you the 2-inch measurement, but once you get into the summer season the soil temperatures don't differ too much from the air temperatures."
Farmers pay close attention to the agricutural weather side of the Mesonet at www.agweather.mesonet.org, he said. Click on "soil" and "soil temperature" measurements are shown by different depths and averages.