soil temperature as its varies with dept

for small depths, say 5-100meters, the soil temp is fairly constant, and equal to the average year-round temperature above soil.

In depths greater than this,soil starts to get hotter as one approaches great depths.
http://www.energyquest.ca.gov/story/chapter11.html

Soil temperature varies with depth due to various factors, including the amount of sunlight reaching the soil surface, the insulation properties of the soil itself, and the heat transfer from the Earth's core.

To determine the soil temperature at different depths, you can use a soil temperature probe or thermometer. Here's a general approach to measuring soil temperature at different depths:

1. Determine the depths at which you want to measure the soil temperature. You can choose specific depths based on your research objectives or the characteristics of the soil.

2. Using a soil auger or similar tool, gently dig a hole at each desired depth. Ensure that the hole is deep enough to reach the desired depth and wide enough to accommodate the soil temperature probe or thermometer.

3. Insert the soil temperature probe or thermometer into each hole at the designated depth. Make sure the probe or thermometer is fully submerged in the soil to get an accurate reading.

4. Allow some time for the probe or thermometer to stabilize and obtain an accurate reading. This may vary depending on the type of probe or thermometer you are using, so refer to the manufacturer's instructions.

5. Record the temperature readings at each depth. Repeat this process for all desired depths to collect a comprehensive dataset.

6. Analyze the temperature measurements to observe how the soil temperature varies with depth. You can plot the data on a graph or create a temperature profile to visualize the relationship.

By measuring the soil temperature at different depths, you can gain insights into the soil's thermal profile, which is essential for understanding plant growth, microbial activity, and other soil-related processes.