Warmer soil temperatures offer the best possible start for your seed investment.
• By Amanda Huber •
The University of Georgia recommends waiting to plant until a soil temperature at the 4-inch depth reaches 68 degrees Fahrenheit for three consecutive days with favorable conditions forecast for the next 72 hours. Most other states use a 65-degree recommendation, but agree that the warmer, the better.
UGA Extension peanut specialist Scott Monfort says, “The soil should be buffered from a few hours of cold temperatures during the night if it is warming back to the high 70s to mid-80s during the day. However, temperatures in the low 70s daytime and 50s at night for more than one to two days will drive the soil temperatures back down.”
South Carolina Extension peanut specialist Dan Anco says, “When soil temperatures warm up into the upper 60s and lower 70s, with a warm outlook ahead, this helps remove the uncertainty of planting and provides better growing conditions overall, provided moisture doesn’t cut off.”
Soil Type And Moisture Level
Besides air temperature, soil type, soil moisture level, presence of crop residue and tillage impact soil temperature as well.
Kris Balkcom, Auburn University Extension peanut agronomist, explains the relationship between soil type and soil moisture level.
“Sandy soils warm up more quickly than clay or loamy soils. The coarse texture of sand has a lower water-holding capacity than the finer textured clay soil. This moisture changes temperature more slowly.
“A clay soil with plenty of moisture is slower to warm up but is more likely to stay at a stable temperature even if a cool front moves through. Sandy soil, with its lack of moisture, will drop in temperature more quickly from a cold front.”
Tillage And Crop Residue
Crop residue and tillage are two factors that also work together to affect soil temperature.
“Cover crops keep the soil cooler for a longer time period by shading the soil from the sun,” Balkcom says. “Tillage, on the other hand, stirs up the soil and exposes it to direct sunlight, which allows it to warm at a faster pace.”
Creating planting beds is another scenario involving tillage.
North Carolina State University Extension peanut specialist David Jordan says, “Peanut planted in beds in conventional tillage will likely have less stress because the soil will be warmer. However, peanuts planted in strip-till and no-till are more vulnerable because soils are likely cooler and wetter.
“I have planted peanuts under cooler conditions and ultimately made a stand, but it took three weeks. The third week was very stressful waiting on the peanuts to emerge. Once soils warm in the spring, they tend to stay relatively warm unlike air temperatures, which fluctuates considerably.
“Seed is the single most expensive input. Yields are generally the highest when we plant in mid-May rather than early or late May and certainly June,” Jordan says of peanuts grown in the Virginia-Carolina area. “This trend is often observed even when conditions are more favorable in early May than what we are going to experience during the next week or so.
“If moisture is adequate, plant more shallow than normal. But no less than 2 inches.”
Monfort offers the following recommendations for planting scenarios producers may encounter.
“If you are planting dryland and are afraid of losing needed moisture, then I would go ahead and plant. With questionable seed quality, wait to plant until it warms up sufficiently.
“Freshly turned soil will be colder than normal, so let the field sit for a day or so to warm up. For strip-tilled fields with cover, soils are typically colder than conventionally tilled fields, so you may want to allow extra time for soils to warm up in this instance as well.
“If you have a lot of acres and need to keep planting, make sure you are planting with good quality seed. Add an appropriate in-furrow fungicide to help with seedling disease, and do not plant more than 2.5 inches deep.
“Additionally, do not apply irrigation during the coldest days when nighttime temperatures are in the 40s and 50s and the daytime temperatures are below 70 to 75 degrees. Add no more irrigation than is needed to activate herbicides,” he says.
Determining soil temperature is easily done with most thermometers. Balkcom recommends digital soil thermometers that record high and low temperatures each day. “You could also use a regular thermometer to measure the 4-inch soil temperature at mid-day, which tends to be a close representation of the average daily soil temperature.”
Studies conducted by UGA show 70% germination after one week at a 65-degree soil temperature compared to 90% germination after a week at the 70-degree soil temperature. Getting off to a good start is worth waiting on the optimal soil temperature.