Introduction

How do flowers and other plants know when to start growing in the spring? How do farmers know when it is safe to plant their crops? Soil temperature plays an important role in both of these decisions. Each spring, soil is heated from above by warmer air and by solar radiation. Once the soil reaches a certain temperature, it is time to plant and grow.

Soil temperature changes more slowly than the air temperature, so there is always a lag time between the extremes of air temperatures and soil temperatures. Because of daily temperature fluctuations, the soil could be cooler than the air in the daytime and warmer than the air in the nighttime.

Soil temperatures also change with depth. The deeper the soil, the more constant the temperature will be. Because of this, when referring to soil temperatures, the depth at which the measurements were taken is also important.

Objectives