OMAHA (DTN)--With the snow gone and air temperatures warming, producers are anxious to start spring field work. Growers are or soon will be tilling their soil and applying fertilizer with the goal of getting planting done as soon as possible. Growers should plant when the soil is in the right field condition and at the right temperature for seed germination.
Growers can measure their own soil temperature by buying a soil thermometer. If growers want to measure their own soil temperature, there are few simple guidelines that need to follow.
Any thermometer that will measure temperature at a depth can be used to measure soil temperature. Thermometers with a temperature scale etched onto the glass tube can be used more effectively than those with an attached scale. Thermometers need to be rugged enough to withstand being pressed into the soil. Care must be taken to avoid breaking glass thermometers.
Sites selected for measurement should be representative of the soil to be seeded. If growers are seeding in a bare, exposed soil, measure under those conditions. If they are seeding into stubble, measure under stubble or residue conditions. Bare soil warms more quickly than covered soil and can be planted more quickly.
Growers need to consider the direction of slope. South-facing slopes warm more quickly than north-facing slopes or level land. Snow melts more quickly on southern slopes. Southern facing slopes will warm more quickly and can be planted earlier than northern facing slopes.
Dry soils warm faster than wet soils. Moisture content is strongly related to soil cover, slope aspect, texture and drainage. Soils covered with residue, have a northern exposure and have higher clay content will dry more slowly than bare soils, soils with a southern exposure and soils with a light sandy or loamy texture.
Measure the temperature of the seeding zone. Since most seed is planted 1-inch to 2-inches deep, the probe should be inserted to this depth. In early spring, while the soil is still cold, measurements at a 4-inch depth indicate whether the soil is still cold or is warming.
Place the bulb or sensing part of the thermometer at the seeding depth. Growers should use a pilot hole to reduce the risk of breakage. The bulb should be in firm contact with the surrounding soil for one or two minutes for the thermometer and the soil to reach temperature equilibrium. If there is bright sunshine with radiant heat, shade the thermometer.
For most crops, there is a temperature range just above the minimum germination temperature at which the rate of germination is reduced. Spring seeding should not begin until soil temperature at seeding depth reaches or exceeds the required minimum. Minimum seeding temperatures for spring cereals - wheat, barley, oats--corn, soybeans and sorghum are 40 to 45 degrees Fahrenheit, 50 to 55 F, 55 to 60 F and 60 to 65 F, respectively.